Sexual maturity varies tremendously from one person to another, so I'll leave that to someone smarter than myself
For everything else, a person should be granted all the rights of an adult at 18. I know it's a oft repeated argument, but it has merit, so I'll repeat it again--if you're old enough to enlist in the military, you're old enough to drink a beer.
That also includes driving. The driving age was set at 16 at a time when young people played a larger role in familial responsibilities, especially in agrarian settings. That is no longer the case.