This is a pretty long article, but it gives good info on what age the average brain is "mature".

http://mentalhealthdaily.com/2015/02...lly-developed/

I recall going to races as a kid, and they were sanctioned by AAA. And back then you had to be 21 years old. I also recall some guys using trickery to drive before they were 21. Like Troy Ruttman, the the Rathmanns, etc.