You answered your own question.
Its not what you drive its how you drive that matters. The reason young drivers pay high insurance is because they are a high risk. That risk could be reduced using tracking/black box technology. It is far more effective than everyone under 25 driving around in 30bhp Reliant Robins. Everything they did in their vehicle would be monitored and if they mess up they loose their license. A similar system is already in place and is effective.
Quite right, it is how you drive. BUT, put the vast majority of young drivers in an aggressive car and they'll drive more aggressively. Less than a week ago we had an 18 year old driver in a Citroen Saxo VTsomething or other who managed to crash it into a wall. It had probably been quite a decent motor at some stage. This one was replete with alloys, big stereo, that was still blasting out when the (first) ambulance arrived, Pipercross (type) filter, exhaust that looked like it had come off a Yamaha R1 and regulation column of manufacturers logos on the leading edge of the doors.
A Traffic Patrol was in the area already after reports of "someone driving like a maniac" round and round the area. Still, an ambulance got there first in response to a 999 call, followed by another four as the caller stated that there were "loads of people in the car". Fire also responded due to the state of the car and several gallons of unleaded covering the floor and the belief that cutting gear would be needed.
The four occupants were aggressive to the ambulance crews and refused treatment and denied a witness's report that others had run from the car. Four of the ambulances left leaving one behind. They were then called back after a girl got out of the car and collapsed with a broken leg and another started coughing up blood and a third was adjudged to have concussion. They also admitted there had been two others in the car who had legged it. Better call up the helicopter to look for them then.
The driver was in an urban area fairly close to home and in a 30 limit, but driving a relatively high powered, light car with an aggressive "attitude".
The driver's attitude is also important and you can have older more experienced drivers still crashing, but if you take 1) a young driver in 2) a "sporty/aggressive" car who is 3) driving at night 4) is with a group of his peers and 5) driving outside the kind of roads he learnt on then as actuaries will tell you, the chance of (probably a) him having a crash is dramatically increased.
As for the black box/trakker type thingy, what happens if a parent is driving? If you give someone a car of limited performance and, don't forget the "aggressive car syndrome" that will certainly reduce his chances of stuffing it. But if you give that driver a faster/more powerful car with a monitoring device how do you know who's driving it?
As for 30bhp Reliant Robins, all I can say is.....brilliant, superb. You truly are a genius, I wish I'd thought of that. You can't drive them fast or they'll fall over in corners and bends, and if you do hit anything head on you'll be impaled on the steering column. Not only that, but it will teach young drivers smoothness and good driving technique.