The idea of getting collector car insurance is to get a better price because they can limit their exposure to claims. The odds are much better for people under 25 to be involved in an accident, why would you still expect to get a discounted rate when you add a high risk driver to your collector car insurance?

Your regular insurance may cover your under 25 driver on their collector car insurance, but I would expect a much higher premium, and I would expect a lot of hassle should a claim need to be made.