Ash is the Highlander. The fearow killed him in the first episode, and he's been stuck as a ten year old ever since.
The official Japanese website says he's still ten, and that makes no sense, but thats what it says.
I feel he's gotta be 14 or 15 by this point. With each outfit change he dresses more maturely, so he looks older now, evn if his model sheet and height haven't really altered.
That explanation aside, I always felt the official ages were off by a a few years. The early official ages always placed Ash at 10, Misty at 12, Brock at 14, and Team Rocket at 18 (what's wth the multiples of 2?) but they always seemed older than that to me in terms of character design and personality, and I felt everything made more sense if you just added 4 years to all those "official" ages.
It really just boggles the mind that they'd set 10 year olds out upon the world, but then, the Pokemon world is a generally nice place where random strangers will feed you for helping them find their runaway Farfetched or something. But sending out a 14 year old, (Which is the start of high school instead of the end of elemetary school) who team up with a 16 year old girl who's on the road to becoming a gym leader, and a 19 something older mentor, (and the Rockets being in their 20s and past their primes) just makes more sense.
And of course, considering the sheer number of siblings Brock has, it makes more sense for him to be not 14 but 18ish.
nd of course, when May came in... she really, really does not look like a 10 year old, 14 would make way more sense with her too. Dawn at least, actually looks 10ish.