Moonlight Amaryllis
♪smoke and mirrors♪
Why, it is all Hanyuu's fault, obviously.
But in all due seriousness, I believe it is because if they aged him in the story, there would be either a. complaints about the character of a children's anime being 15 or b. the complain about the time gap because, "OMG HE'S 13 AND HE SHOULD 17 ASDFGHJ". People will never be satisfied with his age, so the writers were just like, "Screw it!" and kept Ash the same age, because children would be able to interact and understand his personality better because he's 10. All the same, many of us are still outraged at his stupidity, while others adore it...
But in all due seriousness, I believe it is because if they aged him in the story, there would be either a. complaints about the character of a children's anime being 15 or b. the complain about the time gap because, "OMG HE'S 13 AND HE SHOULD 17 ASDFGHJ". People will never be satisfied with his age, so the writers were just like, "Screw it!" and kept Ash the same age, because children would be able to interact and understand his personality better because he's 10. All the same, many of us are still outraged at his stupidity, while others adore it...