I'm 24 (full license from 17) but have no official NCB as I have been driving company vehicles (and my previous
MCS I had on my company's fleet policy from ages 22-24).
Also, I was a named driver on my late father's policy and had to claim when someone reversed into it when it was (legally) parked. Even though there was no question of liability (which the other driver accepted, not to mention my father's insurance company) when I got a quote for my GP from Bell Direct it added £170.00 to my policy! Thieving b*****ds.
However, Bell were still £500 cheaper than the next nearest quote. So, I am now paying over £1500 for my GP for a '10 month NCB accelerator'. Besides their charging me for making a claim on a previous policy that wasn't my fault, they were by far the cheapest. However, they are part of the Admiral Group, who don't like mods, which can be a real pain when insuring a MINI due to the huge number of options. I'm ok though, as the GP is completely as it was when it was built.
Good luck.