I grew up on classical, opera, big band, and folk music in the 60's. It wasn't until junior high school in the early 70's that I started on what's now classic rock-n-roll. I think my first Columbia House 3/free order was Chicago (big-band-ish), Grass Roots (folk-ish), Rolling Stones, and a bonus of the Woodstock album. Pretty quickly thereafter I heard all of ELP Tarkus, and all was lost
To this day I still prefer the synphonic and fusion sides of prog, due to those early learnings.