He has only matured a bit.
What has actually happened to him is that he nearly lost all his sense of humor, has become really less enthusiastic, and the anime itself has become bad which in turn makes his character look bad. Oh, and his voice, and the most important thing - his personality changed - and mostly for the bad...
Sigh...If only the stupidity part was removed as the anime advanced, but not anything else...
I didn't like the fact that he could be really stupid at some times in the first few seasons, but that doesn't put out the fact that I liked his character much better in those first few seasons much more than what he is now.
Like I said, this is not mature - this is a change of personality - and I always like a person based only on their personality, which in the case of the present Ash is not something I like...
This is one of the many reasons I stopped watching the Anime. He and the anime itself was way, way better back then - admit it or not.
