I have been recently watching Youtube for the Indigo league episodes and I have noticed how different Ash is from how Ash is in the newer episodes. He has character development, being an big headed kid, etc. something which a lot of people want in the present episodes but now, he's like that perfect cartoony role model. I have also realized nobody has ever mentioned that Ash is 10 years old since the first episodes, so I have a theory that Ash has aged it's just that nobody is mentioning it. IMO Ash also grown height over the seasons.