Kyo Kara Maoh!/Headscratchers

I just can't figure out, at what speed the Mazoku actually age. I mean, Wolfram being older than he seems is handwaved b6 saying that Mazoku age slower than Humans. But how does that explain Gwendal seeming older than his mother? And shouldn't Conrad be physically older than Gwendal by now?
 * Because most of the time, old men don't get fangirls. Plus, the maids wouldn't have as much fun betting on who Yuuri would end up with.
 * Conrad seems to age at a normal Mazoku rate, since he's remained proportional to his brothers and looked about twelve when his father died an old man. Putting Wolfram physically at sixteen, if rate of aging remains constant then the ratio of years aged to years passed is 1:5.125. That would make Conrad, at apparent age 12, 61.5 years old. Which would make his father roughly between the ages 86 and 96 when he died. At least in the manga, he died at the age of 89. Gwendal looks so old because he's been prematurely aged by the stress of taking on his family title so young, and then fighting Stoffel tooth and nail for control over his mother's throne. And Celi's just got looks that won't quit, like Jennifer.
 * Also, Gwendal has the stress of Annissina.
 * Also, mazoku might not even have a consistent rate of aging from one to the next. They are magical, after all, and life factors might hit them differently than humans. Wolfram and Cheri are both fairly immature, especially when compared to Gwendal and Conrad, so it's possible that they'll look younger for longer, for example.
 * Certain indications exist that aging is fairly individualized. Mostly Cheri & Stoffel versus Gwendal, since Ulrike and Undine are special cases. The evidence is somewhat more conclusive than for Mazoku being functionally learning-disabled as compared to humans, or for their tending increasingly toward flightiness as they reach advanced ages. Gunter is also apparently older than Gwendal. It's possible that in addition to stress it's something in the Voltaire blood, but Gwen's cousin Hube is hardly an uncontaminated sample, with his exile and all.
 * To support this theory, Wolfram concludes that Yuuri must just have 'one of those faces that looks older' when contemplating their age difference. When a sixteen year-old that looks eighty 'just has one of those faces,' something kooky is going on with the aging.