For some people, there should probably also be night-time restrictions. My grandparents both know that their night sight has gone too far for them to be safe driving after it gets dark, but not everybody is willing to accept their limitations that well.
In Colorado, you have to be 16 for a learner's permit, unless you took driver's ed (in which case 15), or something called "Alive at 25", which is like a shorter driver's ed (in which case 15 and 6 months). You have to be 18 for a full license, unless you have had your permit for a full year and driven 50 hours, at least 10 of which have to be night hours.
And people are still clamoring for an older driving age, as if somehow another year not spent behind the wheel makes you a better driver. My kids (if I ever have any) are going to be learning to drive from the moment they are tall enough to see over the steering wheel. The worst experiences one of my driving teachers had while at the DMV were people from New York, in their 30s but still never having had a license. They almost got him killed repeatedly, and wouldn't listen to instructions as willingly as kids.