My first prog gig, Fruupp, was in my home town in 1974. I was 14.
My second prog gig involved a minibus trip to see Barclay James Harvest at Lancaster University, the closest city where you could see well-known bands, on 31st October 1975. I was 16.
I knew of BJH but until I'd bought Live from a friend a couple of weeks before the concert, I hadn't knowingly heard anything by them, though I may have heard Mockingbird on the radio.
My only memento of what turned out to be an enjoyable gig was the tour program. Note that Tom Robinson, a future star with TRB and radio presenter, was a member of support act Café Society (who weren't any good!)