In general terms I would say this.... BUT ITS NOT A SCIENCE OR A CATCH ALL!!!!!!!!!!!!!!!
As you get really old (70 and on) you are lucky if you don't loose an element of awareness, balance and vision and these all lead to problems. Now this does effect people to a lesser or greater extent but there is no denying that it effects you the older you get and will become an issue. My father is a very young 65 and looks about 50 and is a good driver, but in the last few years I have seen him loose his edge and though he would never admit it he has, more so in the night when his vision lets him down.
Younger people (teens and early 20's), and I used to be one so I can speak with a level of objectiveness, tend to think they are much better than they are and take more risks. No quesiton the level of fear is much smaller and the level of confidence much higher (as is the level of reaction too) which married to big tudds can often lead to murder death kill.
No right answer and with all things it depends.