Makes almost no difference to cost, as the compulsory excess on young driver policies tends to be high anyway. A broker pal told me that it's actually cheaper to insure a newer (more expensive) car......
My 17yo has just started learning. I didn't go for the cheapest learner policy, but the one that would be cheapest once he's passed. Admiral offered the best deal, about £700 on a provisional, rising to £1700 on a full, both with a black box. His car is a 1.25 fiesta, 2007 reg (had to get him...