Grade School CEO

A very simple trope. One of the top officers of the Mega Corp happens to be far younger than should be permissible. Examples should be earlier than 12th grade, which is just young enough that it seems implausible. Often the age is justified by the fact that their parents owned the controlling interest in the company, so ownership of it fell to them upon their death.

Subtrope of Improbable Age. Related to A Child Shall Lead Them, where the kid is the ruler of a country. (The two may overlap if the company is an NGO Superpower.)

Advertising

 * The little girl, Susie, in this Verizon commercial. She uses her father's cell phone to turn her lemonade stand into a thriving corporate business.
 * The baby from the E*Trade commercials who acts as a hyper-competent stock guru.
 * This seems pretty popular in advertising. In the UK, a series of TV ads for Velvet toilet paper have featured a computer-animated baby as managing director of a company producing that product, lecturing the adult staff on its qualities. The effect is a bit weird.

Anime and Manga

 * Seto Kaiba in Yu-Gi-Oh!. He won Kaiba Corp from his step-dad when he was a child, and turned it from a weapons-manufacturer to the major provider of the game's central Children's Card Game.
 * Ciel Phantomhive from Black Butler is the head of a massive toy and candy company.
 * In Mega Man NT Warrior, 12-year-old Enzan Ijuuin is the vice-president of the IPC hardware company.
 * Rental Magica has both Astral and Goetia assigned very youngs 'heirs by blood' -- and in case of Astral, magically inept boy who had to learn on the fly -- as acting presidents after disappearance of their old bosses. Justified, as in both cases the alternatives were either worse or unavailable.
 * Watta Takeo from the old Super Robot series Trider G7.
 * Natsu Tanimoto (aka Hermit) in Kenichi: The Mightiest Disciple was one when he was younger, due to his adopted father dying and leaving him with control of the company. In a rather cruel but realistic twist, the company's managers and lawyers immediately conspired together to trick the young Tanimoto into signing over control of the company and its assets to them. It's implied that this stopped soon after Tanimoto was taken in by "The Great Sage Fist", as he's still fairly wealthy at the time of the series.
 * Masako Natsume in Mawaru Penguindrum, who turns out to be the same age as the protagonists.

Comic Books

 * Richie Rich, possibly. In the film version, at least, he has substantial power within his parents' company.
 * The villains of X-Men: Schism are a quartet of obscenely rich kids around 12 years old, the leader of whom takes over for his late father as CEO of the company that manufactures Sentinels.

Film

 * Little Big League: Preteen boy becomes owner of the Minnesota Twins.
 * The Kid From Left Field: Preteen baseball manager.
 * As mentioned earlier, Richie Rich.
 * 101Dalmatians: It's a kid who has the final say on the approval (or rejection) of the game Roger tried to pitch to the company.
 * The Brainiacs Dot Com: Two kids (using investors' money) bought controlling interest of a toy manufacturing company. Trouble arises when the authorities made inquires about the microchip the kids told their investors the money would be used to develop.

Literature

 * Ender, from Orson Scott Card's Ender's Game, is a very young fleet commander. Justified, as he was specifically chosen by the government before he was even born, then educated in a system of schools whose very purpose is turning out little admirals and generals, and finally

Live Action TV

 * Dinosaurs: when Earl becomes a TV Network Executive, one show he greenlights is "Baby Cuddlebunny, M.D." It's supposed to be "Dr. Kirk Marcus, M.D." but Earl decides to make a baby the star.
 * A Bit Character from an early NCIS episode was shown having his own roving nightclub. When a victim is found dead during a party, the team tracks down the owner...to his high school. During the conversation, he lists a bunch of business practices he uses to stay profitable, including subcontracting out the technical work to avoid paying health insurance by himself and having automatic drink dispensers to keep costs predictable. Tony figures that after expenses, the kid clears over $10,000 a night. When they ask about the bouncer on duty that night (the real reason they're there), he whips out a smartphone and Boom! Home number, cell number, business number, and email, just like that.

Video Games
"General Knoxx: "Damn nepotism.""
 * "The Admiral" from Borderlands fits this trope, being only 5 years old.

Western Animation

 * The Simpsons: A show seen on TV is "Admiral Baby", about a baby in command of the Sixth Fleet.
 * Another show they watch is "Supreme Courtney," about a Tween girl on the Supreme Court.
 * Amazingly, there is no law against a child serving on the Supreme Court. The ONLY requirement to get onto the Supreme Court is that you must be nominated by the President and confirmed by the Senate.
 * The Jetsons: The CEO of Contempo Computers.