Yeah, it was high school, definitely a pivotal time. I too sought out bands who played longer songs, and soon realized that it wasn't just that the songs were long, but it seemed that bands who didn't feel the need to conform to the "pop single" mentality had more going on musically, and ultimately that's what I was drawn to.
Usually, that is. I mean, "In-A-Gadda-Da-Vida" is a side-length epic, but it's not exactly prog; it's just a "regular" song with ridiculously long solos. I give them props for doing it, but Side Two is standard stuff and presumably more typical Iron Butterfly. I don't know; I never picked up another album from them.