Pokémon's Ash Ketchum continues to be 10 years old for 25 years — but that does not mean he hasn't developed a little. Ash is changing and maturing along his journey, growing into a better person.
Back within the days in the Indigo League, besides Shiny Pokemon Buy, Ash's personality was almost unrecognizable as compared to his current-day counterpart. The first and biggest of these key traits is his tendency to rush into things headlong without thinking, for example when he attempted to catch a Pidgey by throwing rocks at it inside the first episode.
Another more important part of Ash is his willingness to sacrifice-starting from the protection of Pikachu in Episode 1, Ash has never considered whether it will be life-threatening, but he always knows how to do it right. He also cares about his Pokémon very much and respects their decision-whether it is evolution or love, Ash will not force any of his Pokémon to perform anything they don't want.
But Ash's love of Shiny 6IV Pokemon does not necessarily translate into maturity — particularly since he held not much love for his fellow man at the beginning of the series. As the show began airing from the late 90s, Ash was trapped by some from the thinking in the day and sometimes mocked Misty on her behalf femininity — although she was ordinarily a far more capable trainer than he. Likewise, the Ash with the original series struggled greatly with pride and overconfidence, boasting about his accomplishments while putting little or no work towards those accomplishments.
Ash began to take notice of others more as they left Kanto. Where before he previously had been self-centered and boastful, furthermore discovered joy to help others achieve their dreams, for instance encouraging Clemont's inventions or helping Mallow find Yellow Nectar to generate her restaurant's legendary dish. As a result of growing to look after his human companions more, he grew not just to be able to accept defeat but even sincerely congratulate his friends if they bested him.