I'd say that driving skill is equal parts experience and maturity. Your average 16 yo has the attention span of a squirrel behind the wheel and the emotional conviction that he/she is immortal. Even a couple more years helps some to get past the former.
I made worse decisions at 21 than I did at 16. The only thing that saved my bacon was living in an urban environment, where the average speed is 30 mph and I was constantly impeded by other motorists.