Immortality Begins At Twenty

""You know, for four hundred years, you've held up pretty well.""

- Peter Petrelli Heroes "Four Months Ago"

""Despite what the math says, elves do not gestate for an entire decade.""

- Things Mr. Welch Is No Longer Allowed to Do In An RPG "#1616"

Sometimes being immortal or a member of a really long lived race means that you also have an eternal or really extended childhood or puberty. And that would really suck.

On the other hand, sometimes fate can actually be merciful and aging occurs naturally or rapidly until a character physically reaches his or her mid-twenties, at which point their aging stops and they get to be young and beautiful forever, or at least a very long time.

This seems to be a common feature for elves, even if they aren't technically immortal and just long-lived. A character that's Younger Than They Look may fall under this if they weren't artificially created; sometimes a character looks like a teen or young adult but is only chronologically in the single-digits of age.

Averted with certain types of Undead Child. See also Who Wants to Live Forever? and Immortality. Contrast Elderly Immortal, Really Seven Hundred Years Old. When this fails, you can have either Age Without Youth or Not Growing Up Sucks.

Anime and Manga

 * Vash and Knives from Trigun aged rapidly from birth (by the time they were a year old they were physically around 8), until they reached the physical age of men in their early twenties. Nearly a century and a half later and they haven't aged a day since.
 * The Phoenix Saga of Ranma ½ has both versions of this. Usually the bird takes a hundred years to grow up, but if you force feed it enough it'll mature faster.
 * The Bounts in Bleach are mostly mid-twenties, although there are a few older.
 * None of them seem to look older than 30 or so except one, and that's not because of his actual age.
 * The titular half-youma warriors of Claymore are probably an example of this, the key word being probably. While the few Claymores who do survive beyond the average human's prime don't show any signs of aging, most aren't likely to live even that long thanks to the dangers of their chosen profession.
 * Neo Queen Serenity of Sailor Moon stops aging at 22 (as do the rest of her supernatural friends).
 * Deliberately used in Baccano by . Averted with the rest of them, who are whatever age they happened to be when they encountered the Grand Panacea.
 * Although the novels later reveal that
 * Played with in Hellsing. Alucard was in his mid-forties when he died (just like the Real Life Dracula), but has the appearance of a man in his twenties because he is powerful enough to assume pretty much any form he wants. When his full power is unlocked, he resumes his original appearance (complete with mustache), but quickly resumes his usual form (and later the form of a fourteen-year old girl). The artificial vampirization process used by Millenium also restores their soldiers to a youthful state . Played straight with Seras.
 * Crest of the Stars has the Abh. Barring accident or illness they live to between 200 to 250 years. From birth to 15 they age at more or less the same rate as a normal human. From 15 to 25 years their maturation slows until they're at a point somewhat equivalent to a lander at age 20 at which point they only age very, very slowly.
 * New Cutey Honey takes place about a hundred years after the original series, but Honey only looks a few years older . . . of course, given that she's an android, the fact that she's aged at all is surprising. Possibly justified in that she's a shapeshifter, and may have used her powers to age until her teen years were behind her.
 * In Axis Powers Hetalia it is shown that the Nation-tans age as children, but are usually stuck at 20 or so. It shows Italy as a chibi in the age of the Holy Roman Empire, but adult by World War I.

Comic Books

 * The viltrumite Nolan Grayson aka Omni-Man and his son Mark aka Invincible from the eponymous comic book.
 * Jenny Sparks from the Authority stopped aging at 19 and remained that way for the remainder of the 20th century. Probably applies to some of the other "century babies" too but some of them at least appear older.
 * Wolverine of the X-Men aged normally until sometime during his prime, when his aging slowed down significantly. Stories set a couple hundred years in the future often show him looking like a normal person would at 50 or 60..
 * The rather obscure ClanDestine of Marvel has this in spades. It's not true immortality, as some of them age - just very slowly. The clan patriarch hasn't aged a day since the 12th century.

Film

 * Star Trek: Insurrection The magic radiation produced by the planet's rings takes some time to stop/slow the aging process. So when Picard asks a young boy if he's really 75 he's told "no, I'm twelve."
 * Which makes a bit of sense when you realize that the radiation regenerates chromosomal DNA and through that, the organism. Aging is a result of the telomeres on those chromosomes shortening.
 * Which incidentally contradicts the fact that it cured Geordi's blindness, as he was blind since birth. Age reduction wouldn't affect that.
 * Played with in the film In Time. People are genetically engineered to stop aging at age 25, and continue to look the same until their time - which has become the new currency - runs out and they drop dead on the spot. At one point, Vincent Kartheiser's character introduces his wife, daughter and mother-in-law, all of whom look around the same age. It's also possible to kill yourself through, say,  even if you still have years left.

Literature

 * Subverted in Ian Macdonald's River of Gods - one of the many enhancements given to the so-called "Brahman Babies" is a doubled lifespan. They age half as fast physically, but mentally (or at least legally) grow up at a more-or-less normal pace, leading to apparently ten-year-old night-club owners.
 * A short story set in the same universe points out the rather nasty effect this has on marriages.
 * Dragaera definitely uses this- from what I can tell, Dragaerans are in puberty/teenage from about ages 1-70 but then can be in their twenties or at least the prime of life for a couple of centuries and even to millennia. Unlike some elves though, they do get old eventually.
 * In JRR Tolkien's Middle-earth (Lord of the Rings, etc), even the long-lived human peoples are mature in their twenties. The immortal elves (according to a posthumously published text and thus of uncertain canonicity) reach adulthood in their sixties, but in their first years develop faster (e.g. verbal and motor functions) than their human counterpart.
 * On the other hand, in The Lost Road, the long-lived Númenóreans age more slowly and have an adolescent appearance and mentality when they are chronologically in their forties.
 * If you look into the appendix at the end of Return Of The King, it's stated that elves have much longer childhoods than humans, and hence an elven child may have the mental capacity of a human adult. Apparently it's all relative, in any case, because if you go back to the dwelling of the Valar in Valinor, and the arrival of the three primary elf races, the perspective on growth was very different, due to immortality/longevity being the standard state of being. And so, in effect, the aging process of humans and the races of middle-earth would have been seen as abnormal by the Maiar, Valar, and elven races. However, the overriding description of elves by Tolkien isn't so much that they look like they're in their early twenties, but that they assume an ageless quality over time. The idea is that there is no human comparison for such a state because they are an alien race to the concept of mortality (if elves die on the mortal plane, they find their way back to Mandos' halls, and (usually) end up living in Valinor).
 * Also averted with Hobbits, who routinely live to 100 but mature more slowly in proportion, being considered to reach adulthood at 33. Their twenties or "tweens" are considered equivalent to Men's adolescent teens.
 * In the Kiesha'Ra series by Amelia Atwater-Rhodes, shapeshifters age like humans and then stop aging past 20.
 * Played straight in Duumvirate, where it's referred to as "maximum age".
 * A science fiction story called Start The Clock (available on Escape Pod, IIRC) was all about the results of averting this trope. An ill-defined plague stopped everybody aging (and apparently gave immortality as a side-effect). The worst-hit group seem to be the teenagers, since their hormone overproduction didn't stop, turning most into what amounts to bunch of sex-mad orcs.
 * In Twilight Renesmee the human/vampire will supposedly grow to be 17 in about seven years and then be immortal.
 * And according to Word of God if you become a vampire while pregnant, you remain pregnant for all eternity. Or however long you manage to live.
 * The dragons in The Inheritance Cycle grow up within a few years, despite having very long lifespans. This is taken to the logical extreme in film.
 * Partially used in The Belgariad by David Eddings. The female sorcerers (Polgara and Poledra) apparently stop aging after reaching adulthood, but the male sorcerers all appear as old men. While never stated or hinted at, it is possible that this is actually a conscious decision, as all sorcerers are also capable of shapeshifting.
 * Pretty much outright stated. In Belgarath the Sorceror, Belgarath says that old men are regarded as wise sages while old women are regarded as ugly crones. It's a subconscious decision, but each sorcerer does decide when to stop aging.
 * The dryads also play this straight. Ce'Nedra doesn't look to be much younger than her cousins. She's initially in her mid-teens, and looks it; they're Really Seven Hundred Years Old.
 * Done in The Company Novels, where the immortals go through the immortality process from pretty much birth to age 18 and then stop aging. They have to use makeup in order to look like they are still doing so.
 * In the Mercy Thompson books, all werewolves look to be in their early or mid-twenties, no matter old they were when they were turned. The only naturally born werewolf stopped aging in his mid-twenties, as well. This is stated to be part of their healing and disease resistance magic.
 * Played straight in The Guardians of Time Trilogy.
 * In Joanna Bertin's Dragonlords trilogy, Dragonlords are humans born among humans but utterly sterile, birth marked, and with half-dragon souls; at some point these dragon souls manifest and the Dragonlord is stronger and more magical than most humans as well as able to transform into a dragon, and from that point on they age incredibly slowly. Typically they manifest in the twenties or thirties. In The Last Dragonlord, the Dragonlord mentioned in the title is also called "Little One" because he's the youngest, at six hundred years old. Their leader manifested unusually young, at sixteen, and by this point is visibly old. The little one wonders about just how long she's been alive but doesn't ask.
 * Conrad Nomikos, the main character of This Immortal by Roger Zelazny (if the title didn't tip you off, you haven't read enough of this website) looks 23. He's looked 23 for hundreds of years.
 * In J.R. Ward's "Black Dagger Brotherhood" series, vampires live for hundreds of years. Their transition from "pre-trans" to full vampire occurs at about 25, and they age very slowly after that.
 * Both Played Straight and Subverted in Trudi Canavan's Age of Five trilogy: whilst the White and the Voices stop aging when they are 'chosen' by their respective gods, The Wilds (powerful sorcerers who develop immortality naturally) generally cease to age at the point when they discover the secret. Whilst most of the Wilds are older than twenty when this happens, due to the full emergence of their powers generally happening after puberty, one of the Wilds  is several thousand years old, but has the body of a child of seven or eight.
 * In The Wheel of Time Aes Sedai use an Oath Rod (originally produced as a Restraining Bolt for criminal mages) as part of their Initiation Ceremony. As a side effect, it makes them "ageless," which means "attractive." Oh, and it cuts their lifespans in half, which they don't know until they meet wrinkled mages who are 400 years old.
 * Fans who have way too much time on their hands have deduced (Based on in-book descriptions of the oath process and of the Aes Sedai themselves) that the cause for the "ageless" appearance is that, in addition to aging more slowly, they never get wrinkles (They explicitly compared this to botox).
 * Inverted in Sean Mc Mullen's ''Voyage of the Shadowmoon", wherein Laron is a perpetually 14-year-old vampyre. With acne and a stuck-on beard. It sucks.
 * Inverted in The Meq. The Meq attain immortality at 12 and lose it when they are ready to mate.
 * In Kim Harrison's The Hollows it is implied that witches grow up like humans and age little for about a century after they reach their twenties, resulting in a natural life span of about 160.
 * In Honor Harrington, prolong recipients are "frozen" at a different age range depending on which version of the treatment they got: mid-forties for 1st, late 20s for second, and early 20s for 3rd. The freeze extends lifespan to the two to three century mark. It also has the effect of extending stages of development; Honor Harrington herself was a bit of an awkward adolescent, gangly and horse-faced, until at least well into her 30's. Such treatments are new enough during the period when most published stories are set that we don't actually get to see any characters who are 250 years old but look "only" 65 or so, but first- and second-generation recipients of the Prolong treatments do seem to get a prolonged middle age as well as the usual prolonged young adulthood.
 * Joan of Arc in The Secrets of the Immortal Nicholas Flamel was turned immortal when she was a teenager, so she has this. Averted with many other immortals, though.
 * Played for Laughs in Guards Guards, when it's mentioned that dwarfs live up to around 300 and only hit puberty around 55. The human Carrot's adopted dwarf parents find it hard to cope when he reaches young adulthood at what, to dwarfs, is "playgroup age".
 * Justified in Dirge for Prester John. People take their third pilgrimage to the Fountain of Youth at thirty, freezing them in time at that age.

Live Action TV

 * Inverted in an episode of Moonlight where a vampire who was turned as a young adult has to spend the rest of his immortal life in the midst of puberty.
 * Adam Monroe in Heroes
 * Also Claire.
 * Adam says in the webcomic that he stop actually ageing (at least, he noticed it) when he was about 40. His ageing had probably slowed down before this.
 * For Sylar, though, it's justified- he acquired his powers of unaging-ness when he (or the actor playing him) was in his twenties, so it makes sense that that's the age he'd stick at.
 * Stargate has this to an extent with the Ancients. While they (presumably) grow up at a normal rate compared with regular old humans, once they reach maturity they seem to be capable of staying this way for a very, very long time (millions of years if they happen to be encased in ice, as was seen in one episode... though there was limited degeneration, the Ancient in question was still perfectly able to walk, think, and understand modern humans).
 * Highlander the Series both averts and explains this. Immortals are always frozen at the age when they died, so you can get child immortals, but because immortals also tend to hunt each other down, the children don't last long, so you don't see many... the ones that survive the first few years... tend to be off.
 * The Star Trek: The Next Generation episode "The Child" has Troi's baby growing up (more or less) within a day or two. Of course, he was an alien intelligence hijacking Troi's body, but that's neither here nor there...
 * In Young Dracula, vampires age normally until they turn 16 years old. From the looks of Dracula, they probably still age a bit after that, but not much.
 * Becoming Human averts this. Adam was turned at 16 and is stuck as either a schoolkid or someone in a badly-paid school-leaver job forever, since he'll never be able to pass for much older.
 * In Kamen Rider Double, Philip  Towards the end of the show, he's confirmed to be seventeen years old, but Delusion Diary #11 hints that he won't age beyond that   It may or may not be true given that the scene was part of Shotaro's daydream.
 * In Can You Live Forever?, Adam finally achieves this after a long series of experimental medical procedures using Sufficiently Advanced Technology.
 * In the Star Trek: The Original Series episode "Plato's Children", an alien race that based itself on Ancient Greece genetically engineered themselves to stop aging at about 30-40 years old. (When Spock informs one of the female aliens that she looks a few years older than the age at which she officially stopped aging, she's a bit miffed, despite being thousands of years older.)

Tabletop Games

 * In the Fourth Edition of Dungeons and Dragons, races that have lifespans greater than that of a human (for example, eladrin) follow this trope, maturing normally until around the age of twenty and staying like that for the majority of their lifespans. Previous editions gave the age at which they reached "adulthood" but no indication of the rate of maturity (which led to questions like, "is a one-hundred-and-ten-year old elf as emotionally mature as a fifteen-year old human?" and "is it wrong to bang an eighty-year old elf?")
 * At least a few sources suggested that elven infants mature fast enough that elves probably aren't in diapers for twenty years, Order of the Stick not withstanding.
 * Adverted hard for half dragons (in some version) who may not have left adolescence by the time others have died of old age. This is in line with dragon aging where 101 years is considered adult, even considering the half part that's adulthood at 50 ish.
 * In GURPS each level of Extended Lifespan doubles the amount of time spent maturing. However, Fast Maturation is available as a zero point ability with each level cutting time to mature by half causing the character to spend that much more time at their prime.
 * In Exalted, Exalts (who may live anywhere from a few centuries to a few millenia, or even eternally depending on type) stop visibly aging until the very end of their extraordinarily long lifetimes. Since the average age of exaltation ranges from late teens to mid-thirties (there are exceptions of course. The youngest exalt was a preteen and still is after 1500ish years, while one of the oldest to exalt was over 60), they somewhat fit within this trope.
 * Also, the Terrestrial Exalted age more continuously and gradually over the centuries (or else their Exaltations would leave a good number of them as semi-eternal children), but do not move past their (physical) fifties or so until their lifespan draws close to an end.
 * Strangely enforced for Infernal Exalted; part of the deal is having vitality restored, so the general body warping process of the chrysalis grotesque includes being brought back to a physical appearance that roughly resembles their twenties (ironically, the Infernals are, by default, the shortest lived Exalted, with a mere 150 year lifespan).
 * Inverted in Promethean: The Created, where mortality begins at twenty - a Promethean who completes the Great Work becomes a human in young adulthood, and can expect a normal lifespan from there on out.
 * In the AD&D 2nd Edition setting Birthright, people can inherit divine bloodlines, which are generally assumed not to manifest until puberty. One such power is extreme long life, from five to one hundred times longer.
 * The New World of Darkness book Immortals features a group of beings called the Purified, who became immortal through one of several rituals that involved dying and then coming back to life. No matter how old they were when they performed the ritual, when they come back to life, they always come back in a body that is physiologically in its mid-twenties.
 * Juvenat treatments in Warhammer40000 retard ageing, but do not affect maturation--thus, nobles, Inquisitors, and other important people can appear to be in their thirties or forties at two to three hundred years of age. The treatments are not perfect, so the appearance of a very healthy 40-50 year old is most common, barring additional surgery.

Video Games

 * Raine and Genis in Tales of Symphonia. A bit jarring in Raine's case as she.
 * As discovered later in the game, both had their aging halted at twenty-something., on the other hand, got it stopped when he was still a kid, and had to learn a special technique to make himself look older.
 * Apparently the case for True Ancestors in Tsukihime. Arcueid looks to be slightly older than Shiki does, and looked that way around eight hundred years ago as well. Fridge logic implies that either she grew from infancy to full maturity very quickly, or she has always been an adult.
 * The branded in the ninth and tenth Fire Emblem games age according to their beorc heritage until they turn sixteen, at which point their aging processes slow down to match their laguz heritage.
 * In the Suikoden series; the True Runes keep their bearers from aging at all, leading to one character who's been physically a child for over three hundred years. The effects lasted long enough that they didn't even age while  in Suikoden IV. Needless to say,   a bit annoyed about this.
 * However at least the runes allow bearers to hit puberty before the whole immortality thing sets in. Otherwise characters like Luc and Sasarai who are implied to have had their runes since birth would still be infants. The theory is that the rune stops aging at its prime as defined by JRPG standard (i.e. mid to late teens).
 * Pretty much how the aging process for demons native to Veldime works in Disgaea 2 Cursed Memories.
 * Averted with non-Veldime demons, who typically have 500 years worth of puberty to look forward to.
 * Angels also have the same problem as demons from netherworlds apart from Veldime. Flonne is the oldest from the trio of main characters of the first game at 1509 (Etna and Laharl are 1470 and 1313 respectively) yet all of them look like there's no real difference apart from height.
 * Touhou Project, especially in fanon, plays with this trope for all it's worth, thanks to it's Loads and Loads of Characters who are Really Seven Hundred Years Old. The scarlet sisters were born vampires, and Can't Grow Up, as are all of the fairies in the series, who are refered to in Perfect Memento as having at most the appearance of a 10-year-old child. Most of the others, however, are adults who have lived thousands of years, and include some apparent teenagers who are truly immortal. Yukari, especially, (thanks to dressing up and occasionally playing like a younger woman than she appears to be normally) gets jokes from fandom about being the "old maid" (in spite of only being a couple thousand years old, which is fairly normal by Touhou standards) by some corners, and having her boast that she's (eternally) seventeen by others.
 * The fairies may not fully fall under this trope as they are elemental embodiments that are reborn each time they die (which may occur with the changing of seasons according to some interpretations) rather than being immortal or long lived.
 * After her powers manifested, Aya Brea of Parasite Eve actually got physically younger. While she actively refused to use her abilities between games, by the time Parasite Eve II rolls around, Aya is permanently 21.
 * Ms. Fortune from Skullgirls has something like this. A stolen gem that she swallowed granted her immortality plus a wildly accelerated Healing Factor -- which explains how she survived being chopped to pieces by the Mafia thugs who tracked her down to get the gem back. She hasn't aged a day since her supposed "death", and has worked out a way to use her newly-detachable limbs and head to her advantage in combat. Pity about the scars, though.
 * Played with in Mass Effect. Averted by the asari, who are generally thought to leave childhood at forty, and considered mature adults at 80. Krogan play the trope straight.
 * Miranda states that because she was heavily genetically modified, she will likely live 50% longer than a normal human, and it is stated that her body is in its twenties even though she is in her thirties. She makes no mention of whether this affected her growth rate as a child, though  grew up having a normal life, which would presumably be impossible if all ageing happened slower than normal, so presumably they play this trope straight.
 * from Solatorobo zig-zag this trope together. plays it straight, appearing to be a young adult despite his age, but  averts it by being stuck as a teenager.
 * Nobodies from Kingdom Hearts appear to have a case of this. Word of God states they don't age, however the Nobodies who lost their heart at a young age all seemed to age normally since the time when they would have become Nobodies, while their fully-grown counterparts haven't aged a bit in the intervening decade-or-so.

Webcomics
"Haley: I can't really see the downside of --
 * Read this page from Eight Bit Theater; the lower left panel is fairly creepy.
 * In Drowtales, Drow age at 1/2 human rate and stop aging at around 60, thus making them the physical equivalent of a 30 year old human.
 * The elves of Elf Quest grow to maturity at about the same rate as humans before entering "the long golden afternoon" of elfin longevity.
 * Averted and lampshaded in Irregular Webcomic, when one of the characters in the Fantasy theme (Mordekai) asks the elf Alvissa why her race hadn't outbred everyone and overpopulated the world. Her answer: "Elven children breast feed for 30 years, teethe for 20 years, throw tantrums for about 100 years, and don't take to toilet training until they're about 200... Elves invented effective contraception before we could use fire."
 * In Inverloch, elves seem to age at the same rate as humans do up until they are fully mature, and then they stop aging. Except for the Severed, who are mortal and continue aging at the same rate as humans until they are cured.
 * In Pandect, Aces (animals with human souls and the ability to switch to a human body) stop aging entirely in their animal bodies, and the human body ages to about mid-20s and then remains there for the rest of their (very long) lives. Justified in that they have to earn Ace: the prolonged period of youth is part of the reward.
 * Genetic elites in The Cyantian Chronicles, though their age catches up to them quickly as they reach the end of their lifespan (ranging from 120 years in foxes to nearly a millennium in wolves).
 * Also elite wolves don't reach their full height of about 7'6" for several decades, as Darius and his classmates are teenagers or mid-twenties they tend to be pretty short (~6 feet) by their species' standards.
 * Very common with the long-lived races in Dan and Mab's Furry Adventures, pretty much every creature race that looks like beings effectively stops aging in their 20s.
 * In the case of the Cubi their major abilities do not awaken until their early 20's, and as one of those abilities is shape-shifting they can look any age they wish for the rest of their lives.
 * As demonstrated by Cyra herself here.
 * Averted amongst elves in Order of the Stick, according to Vaarsuvius:

Vaarsuvius: Twenty years in diapers.

Haley: Oh."

Real Life

 * Truth in Television, as far as medical science is concerned. Growth/maturation (which typically ends around 24 or so) is different to aging - the second is caused not by hormonal changes but by other factors. Thus, if somebody ever comes up with an immortality pill, it'd essentially "freeze" your age in your mid-20s. "Slowing down" the entire process, thus increasing the time spent in childhood, is presumably doable genetically, but pointless for extending someone's life - diseases already exist that have a similar effect (hi there, Gary Coleman!) but they don't increase life expectancy (quite the opposite).
 * There's an aversion, though - there's a girl who has a genetic condition that ages her at one twelfth of the rate of a normal human. She's 16 and still stuck in the body of a 1 year old, and for that matter the mind.
 * The really bad part about that though is that because, as just stated, maturity and old age are caused by different things in your body so she might not actually live any longer than normal. Even if she lived to be a hundred, she would only be eight years old, biologically and mentally.
 * Religious example: Mormons (and probably other denominations believing in a physical resurrection at the Last Judgment) believe that the dead will be restored to appear as they did/would have in the prime of their lives.