Only thing about classic car policies is that you don't earn ncb, and you can't drive other peoples cars.
Having said that, I'm 19, and have been driving my 1990 Mini Studio 2 since i passed my test at 17. I paid £550 last year, and i'm expecting it to go down in april, when i renew.
Even better, my car's a 1.3 and will kick a modern hatchback's arse!