Well, when I started listening to rock at about 12, I was all about Zeppelin and AC/DC, nothing else. One of my best friends was a huge fan of Rush, Kansas, and Yes but those bands really didn't do much for me.
My sophomore year in high school, I was eventually convinced to give a Nightwish CD a spin. I did, and I loved it. Within a few months, I was completely and totally into Symphonic and Power metal. Later that year, I joined a band with my best friends (who listen to a ridiculous amount of prog) and guess what? They wanted to play Rush.
So, over time I was indoctrinated into the wonderful world of prog, and I am very grateful for it. My junior year was the first time I really discovered Opeth and Dream Theater, and those 2 bands really were the ticket to me enjoying prog as much as I do now.