Now that we've seen what Ash will look like in the newest season of the Pokemon anime, once again discussion of one of the show's greatest mystery flares up: just how old is Ash Ketchum supposed to be, and why does he almost never seem to age?
"Almost" is important there, since the newest version of Ash does seem slightly older—mostly, it's the teeth, as TheJWittz notes here. But otherwise, the show seems to perpetually keep him in the 10-11 range, even though it's been airing for over a decade. It's kind of absurd! At the very least, you'd think the show would keep it consistent, but nope. They don't.
TheJWittz explores a few theories as to why Ash never seems to age here. My favorite is the Ho-Oh one, since it's kind of idyllic—Ash never ages because that's his eternal happiness! Just, you know, forever battling (and losing/sucking at being a Pokemon trainer, apparently...so maybe that doesn't hold too much water). Still, it's a way better theory than the silly "Ash is in a coma" idea, if you ask me.
What do you think? Should Ash age? I'm mostly interested in the idea because that might mean a slightly more mature show, but hey, it's not a show that's aimed at me. Either way, feel free to put forth your own theories as to why he seems to never age, too. I think maybe he just drinks Rapidash blood.
Ash Ketchum's Age - Pokemon fact of the day [TheJWittz]