What, are you kidding? Taking Ash away from the Pokémon show is like... taking some other main character from a popular show. Remove him completely? No way. Ash Ketchum is here to stay, get used to it. If you're tired of seeing his face, don't watch the show or watch Pokémon Chronicles.
Also, just because it's taken this long to see Ash travel to Sinnoh doesn't mean it's taken Ash the same amount of time. He's constantly on the move; we are only told of his adventures once a week (now it's like every day or something, but that's cause Diamond and Pearl are on the way).
In Ash's time, it hasn't taken him this long to do whatever it is he's done. Granted, it's not been a few days or whatnot, but certainly not 10 years. He has gotten older, but not so much older that we notice a difference. It would make it a little more believable if he were a little taller and slightly more manly.
And he started his journey when he was ten, the day he was able to become a Pokémon Trainer. Voltorb clock ftw