My only radio was my AM-only alarm clock. There was a radio in our kitchen that was AM only too. My parents weren't music lovers but my mom would listen to stuff like Engelbert and Tom Jones. My father had some albums, like
Elvis, the Mamas and the Papa's, some Johnny Cash and of course "Sing along with Mitch"

Lots of singles. Whooly Bully, Roll over Beethoven were my favorites. And Ahab the Arab...lol
That was all I really knew of music, along with crappy AM. I don't know how I found out about FM. I think it I read about it in a newspaper or magazine. You are so right in saying that the impact can't be exaggerated. I asked for a radio for Christmas and got this little red thing, probably from Radio Shack, and could not stop listening. So much music I had never heard of. Just incredible. Not sure how old I was. Probably like 8 or 9, maybe a little older.