Will probably get a load of hate over this but whatever...
They should change the "standard" age for driving to 21, however you'll still be permitted to take your test from 17 and then drive as you currently do. The difference would be that, between the ages of 17 and 21, your license to drive would effectively be a priviledge which, if abused, would be revoked.
Basically you'd be allowed up to 5 points on your licence before your 21st birthday. If you reach 6 points then the "priviledge" is revoked and you lose your licence until your 21st birthday.
This would seriously focus the mind of young drivers. If you want/need to drive between the ages of 17 and 21 then fine, you can, but you'll need to be careful so as not to forfeit that priviledge. I appreciate that someone who doesn't bother taking their test until they're 21 would also be "as new a driver" as a 17 year old but I maintain that the average 21 year old is a darn site more mature, sensible and less hormone-imbalanced than the average 17 year old.
Flame away