Will probably have to wait until I'm 25 I think until the price will be heavily reduced?
In my experience, there's no age-related drop, per se – what they're looking for is experience and insurance history, among the many factors that are taken into account. I've had friends who haven't passed their test until 30, 35, 40, and they've all faced similarly high prices out of the box, for the first few years at least.
In my case, I had a classic as my first car at 17 but had it insured through a conventional policy, which accrued a no-claims bonus; it was £1,800 for the first year, but it dropped to £800 with one year's NCB, and then down to £500, etc. Averaging out the cost over those three years helped blunted the initial high price, for one thing.
When I subsequently got my first Corvette at 21, I then insured that using a specialist policy – which didn't accrue conventional NCB, nor could I use my accumulated NCB on it. However, the company did take those years into account, and I ended up paying some £500 again. And, no, when I reached 25, the price didn't magically drop, either. It hovered around that £500 mark for a long time and didn't really significantly until several years later, but that was more due to a change of postcode and insurers than anything else.
Perhaps it's worth pounding the phones again and seeing what options might be out there, or looking at a later Corvette? A C4 might prove cheaper to insure, I don't know...
Alas, that all said, there are many factors in play when it comes to insurance, so anyone else's experience might not be of any real help. But best of luck to you, in any case! I hope you can work something out. And keep at it, regardless; even if it takes time, you'll get what you want.