HIC can insure under 25's on VR's (under 21's may struggle though) but being a broker the various companies we use to underwrite the policies have different criteria so it may be the particular company/scheme your mate is with would not (although i cannot think of any off the top of my head that would not, especially if he has been driving the types of car you mention).
Same with driving other cars, depends on the underwriter - some we use allow it from 21, some dont allow it for anyone under 25, there are other factors too eg occupation (normally cant get it if work in motor trade etc)
Martin
