I think he is 12Sayuri no Hoshi said:Supposedly, Ash does not age according to the officials at Pokemon.com. They compared him to Mickey Mouse--who is over 75 years old--but does not show signs of aging. "He's an icon; a legend," as they said. We all know that when he started out on his journey, it was on his tenth birthday. Then, he said he couldn't believe it had been a whole year since he had been in Viridian City--that implied to a lot of people that he was at least 11 years old. Most still think he's about 15 or 16 years old. In one episode--"The Fortune Hunters"--Ash, Misty, and Brock got a fortune book and they could look up their horoscope and whatnot according to when their birthday was. So, apparently they have birthdays; but, they do not seem to be celebrated or acknowledged. I guess that Ash is ageless as they say...or is still 10 (or maybe 11) years of age.
There was the short in movie 3. Ash said"Pikachu, this is the day a year ago where we met." It has been a long time since that movie and now.