some of our policies offer it from 19 and up, most 21 and up. You dont have to be fully comp (dunno where everyone gets that idea
) its available on TPFT too, you just have to be old enough, hold a full licence and have an acceptable occuaption (not motor trade etc).
There is no limitation on the type of car (but it is cars not motorbikes, quads, commercial vehicles etc) but bare in mind its third party only on other cars so if you stuff your mates Ferrari in a ditch he aint gonna be too happy!
The car cannot be registered to yourself, it must be insured (eg by the owner) and you must have their permission.
No it will vary massivly with insurers as to whether or not you get it.
Martin