Always ? Since you were 17 ? I doubt it
I never said from 17, at that age it cost me £1500 3rd party. Let me clarify.
Mine has always stated on the policy document that I am covered to drive other vehicles 3rd party, but only since I could afford fully comp insurance which I've had since I was 22. I have never asked for it or used it either.
Edit: That was 10 plus years ago and I know the under 25 clause was implemented across the board not long after that, I think around 2005ish?