I dunno that even the 90bhp idea would work - i think it should be down to insurance group and certain cars.
Cant drive anythin over group say 7 till you're 19, then group ten till 21 then whatever you like.
I know some younger people drive powerful cars and are perfectly safe, infact im only 24 myself and had an mr2 turbo at 19, but i honestly wouldnt have minded waiting, knowing a few less people were dying every day