>>28559555To be fair though, it's highly possible that Ash was supposed to age throughout the series. Except for the first episode that has stated Ash's age (and then later during the first episode of Best Wishes, which has been stated to be an attempt at re-marketing the series with different ideas), it was never brought up again.
Throughout the series, you could see Ash's height change compared to some of the other characters. So it's possible that Ash was indeed 'stealth growing' throughout the series, but Best Wishes undid that.
