Except by deductive reasoning. Ash stated at the beginning of the series that he is ten years old. At the beginning of AG, which takes place at least three years later according to canon, May says that she is ten years old. The official website says that Ash and May are the same age. The only way this is possible is if the characters are ageless in the "normal" timeline of the series (ie flashbacks don't count).
If this is true, then that would mean that we will never see Max in his own special and that the anniversary in Pikachu and Pichu never happened, which is obviously not true. As for the website, it might be an error. Websites have been known to provide inaccurate information, even official ones. Just look at Pokemon.com. But this is all beside the point.