There’s also a lot more claims in general by under 25’s and also as insurance is free on the scheme they have to take into account all post codes some with more claims then others and average costs and risks.
I know my own kids that are under 25 pay a ridiculous amount of money to insure a car in the south east. So much so they have to pay monthly and that is for cars below 150bhp and the lowest insurance group possible.
Also they have massive excesses on their policies where on the scheme it’s only £100 if you make a claim, not if a third party claims from you.
Then breakdown cover on top, servicing parts it’s expensive to drive when you’re young.