Driving should be 18 and over, if not more. In my case, I obtained my drivers license when I was 18, and I still wasn't as responsible as older drivers. It seems that the older you are, the more responsible drivers will be. On top of that, drivers under the age of 18 have little to no responsibility if something were to happen, because they are not adults.
While an 18 year old may be more mentally mature, they may not be as well. The main factor with younger drivers is a lack of driving experience and practice. Having a higher driving age will not change the lack of experience, and could possibly backfire. An 18 year old would likely be doing more driving than a teen (with work, school, etc) and would then have less practice.
No, a driving age of 18 would not be more effective, because students do not learn how to drive at 16 automatically anymore. Anymore, young people only learn how to drive if they need to help their parents with transportation. They are educated on safe driving, and they gain valuable experience at a young age.
I believe the time between 16 and 18 is the ultimate time to learn how to drive. This eliminates the problem of having to have your own car, since generally at that age teens are still at home with their parents. This allows teens to drive and learn over time before going out on their own or moving away for college.
Driving at the age of 18 is no more or less dangerous than driving at 16. There are drivers who did not get their license until much later who are still just as susceptible to accidents as younger drivers. The key is experience and skill. If responsibility were required, I would suggest an older age to start, but that is what insurance is for and premiums support that theory.