Personally I think an element of psychometric testing should be introduced as some people, no matter how old or experienced, really shouldn't be in charge of a kiddies tricycle, let alone a car.
For example regular motorway users will be aware of the many supposedly 'professional' drivers who drive absolutely abysmally, much worse than a clued up teenager: how often do you see a line of HGV's being driven flat out on the limiter at less than a car's length behind the one in front, while the drivers stuff their faces or yack on their phones? Yet these are drivers with many years and miles of experience who should obviously know better....but they seem oblivious to the danger to themselves, and, more importantly, others, and don't seem to have learned anything..........yet a properly switched on but inexperienced driver given the right mindset (pass-plus is good) will learn and become a safe and considerate driver.
As in all things- it's not the age, it's the attitude.