I really don't know the answer Mike......if you put up the age, then they will pinch cars. Restricting speed/power could lead to no power in a life/death situation.Really large draconian penalties for those caught
?? Maybe 
Lets face it, disqualifying people does not work....watch any of the Road Wars type programmes, and you will see how many 'erberts' are driving with a dozen bans in place....so they go to court and get another ...duh 
I really wish I knew an answer
Still can't believe a learner on the phone with a driving school
The need for power in life / death situation is a bit of an old cliche really. If a situation arises where a powerful car CAN make all the difference, only experienced drivers would know how to use that power effectively, as it may not be a case of just booting it. These occurances are rare anyway. I can confidently say that in well over 20 years of driving, I cannot remember even one situation where a more powerful car would have kept me out of schtook. Better brakes, yeah maybe. Also no situation whilst in a powerful where I thought "thank god for a powerful car". One should be driving appropriate to conditions, experience and the cars' capability.
Furthermore, if general driving standards were higher and people left time for their journeys, left space betwen them and other vehicles...and...and...and.... then the need for power would not be there at all, except for a bit of fun.
As for what to do.
Minimum amont of lessons from qualified instructors
Instructors re-tested frequently
Spot checks on driving schools, like they do for MOT stations
Low powered cars for the first 2/3 years of driving, then up the power for another year, then unlimited after that.
Re-test every 5 years mandatory. (Not exactly like the original test) Don't pass? Revoke license.
That should help
