Most tend to be 25 iircHe wont be able to drive other peoples car. Most if not all insurance companies only allow this for people aged over 21. I very much doubt you'll get less than that, you could try adding your parents as secondary drivers which helps quite a bit with many companies.
He can afford it probably because he is on mummies insurance policey and not the main driver.
With bell you can, you usually have to pay quite alot more though (£100+)
also Quinn direct used to, but if you are planning on insuring a cheaper car and then driving an RS on the DOC extension this is naughty!