Their parents let them do too much too soon. Because parents allow their children to drive without restriction, because parents hand over the keys to a car on a child's 16th birthday, a lot of kids are driving without sufficient experience. Learning to be a safe driver takes time. Some legislators think all it requires is passage of a driver education course. Whether kids start driving solo at 16 or 17, experience is a crucial factor.
Maturity is another.
Some teens are mature enough to drive at 16, some at 17, some at 18, and responsible parents will treat their teenagers accordingly. The Atlanta Journal-Constitution recently published an excellent analysis of the state's failure to keep dangerous drivers off the road. Typically males between 20 and 30, these drivers have lost their licenses for multiple traffic offenses including drunk driving, reckless driving, speeding and other offenses. Most have also had multiple accidents. It would seem prudent that before the state passes new laws it enforce those already on the books.