New Pokémon English Dub sucks, but why Ash is still 10 years old in Pokémon Diamond and Pearl?

What makes you think he is still 10? They never say that he is.

they can't keep up with their own storyline. the fact is that ash has been on his "adventure" for a few years, one reference was in the third pokemon movie short when he said that it was over a year since he met pikachu many of them being when misty kept reminding ash that it was "weeks" since he caught anything new.

.......i liked the series when misty was on it..........may and dawn suck!(expression)

probably for the same reason that Shinichi from Case Closed is still stuck in the body of a elementary student after 12 years of the manga being published- it's convenient. Pokemon is targeted at young kids and the hero should be as close in age to them as possible- meaning somewhere around 10-12. Everything above would become another genre. But unlike other series that work on an established fanbase and try to keep track of the audiences age (see Naruto with the time leap and similar series) or star borderline teens as protagonists (see bleach and similar) Pokemon operates in a different mode. The producers practically calculate to lose viewers after they reach a certain age, however they replace them with new viewers that have reached a certain age. That's only possible if a series is almost a tradition- which pokemon is without a doubt.

I guess the company that makes pokemon didn't want to bother keeping track of his age. The whole story line really revolves around pokemon.

Here's what wikipedia said:

At the beginning of the series, Ash was 10 years old, and later, in the episode "The Battle Of The Badge", Ash said that it was a whole year since he and Pikachu had visited Viridian City, making him 11. Furthermore, in the short called "Pikachu & Pichu" which was attached to Pokémon 3: The Movie, he said the day when the events depicted in the short took place was the anniversary of the day he met Pikachu, meaning his age at that time would be at least 12. However, two seasons later, the official Japanese Pokémon website reported that Ash was the same age as May, who was 10 years old at the time. This and the fact that the two are at the same height suggests that both of the characters are the same age.

That always bothered me too

i agree