We should have staged licences like they do in some US states. We do it in a small way with motorcycle licences so it could be done.
I had a 'quiet word' with a VI form student who was using the school parking as a race track. Pointed out that the parents from the primary next door walked through the car park with their children, it hadn't occurred to him.
I think once you pass maybe you should be limited to one passenger unless the other passengers are a) over 21 and b) have a driving licence themselves, after 6 months or a year this could change if they have not been involved in an accident.
So a 17 year old could pick up parents from a pub after Sunday lunch but not take a bunch of friends out for fun.
I think other things could be done such as only allowing a new driver to drive certain cars, or only certain cars when not accompanied by someone over 21.
Something like a smart car, small engine, lower top speed should be OK. I know not all teenagers can afford their own car, so not ideal, but it would have the advantage that any other driver on the road would start to think 'new driver' when they saw one.
With motorbikes you can either start with a 125cc at 17 progressing to a larger bike at 21. If you want to go directly to riding larger bikes you have to be 24.