Tails also matured as a character as his duties as a side kick ended with Sonic Adventure, where he went toe to toe with Robotnik and defeated him alone.
This is also possible in Sonic the Hedgehog 2, the first game he was in. Also the stories in Sonic games suck, so you are thinking too much.
Not sure why you want his voice to sound older when they are just making characters more independent.
In my opinion, with Sonic Adventure they were trying to make all of the characters more independent because they wanted to branch out with spinoffs, like what Mario does with Yoshi, Wario, even Luigi and Peach games now. However, shit happened and they had to scale back their projects and plan them for multiple platforms.
Whether it is Sonic Adventure 1 or 2 or even Yakuza all games are full of plot holes, what the writers hope is to have you so immersed in the action that you don't notice them.
Whaaa?
What plot holes are in Yakuza games, and where do you get off saying
every game ever made has plot holes in it? That is one of the most ignorant things I have ever read on this site, and there have been a lot.