The problem with a "Doesn't age" theory is that the character DID age - right up until Ash's tenth birthday, or their meeting Ash, whichever happened second. The notion of Ash having gained an aura of Age-B-Gone on his tenth birthday is just plain on the wrong side of too much. (Evidence that the characters did age : Ash DID have a tenth birthday, and we saw flashbacks of brat-Misty)
In the Simpsons, it'S acceptable. After all, the Simpson are generally non-linear - that is, a 15th season episode can be sneaked in the 3rd season with little to no plot problems, because there is NO overriding storyline. In fact, if it wasn't for the (limited) number of summer episodes and X-Mas and Halloween ones, we could pretty much claim that EVERYTHING in the Simpson is happening within the same year - so it's not the character who's ageless, it's just the story which is being recast in a modern setting each year. Plus, the Simpsons is comedy, which Pokémon isn't.
Personally, I simply prefer to take the anime's ages with a grain of salt, and the graphical representation the same. For animating convenience and so forth, Ash has to retain the same look, fine. However, that should not be taken as indicative of the age he would be in Hoenn.