I'm 27 now, so the internet was just getting going by the time I was a teenager. I never dreamed of looking up porn on the internet, I guess, but I had become an evangelical at 14. That had a lot to do with it.
However, I was a filthy little 8-12 year old. I may have been sexually dead by my teens, but I LOVED dirty things when I was really young... and porn had nothing to do with it. I had a very corrupting girl friend down the street, and we would pseudo-masturbate when spending the night at each other's houses... no porn, but we built a fort out of boxes upstairs that had all kinds of sexual references taped on the walls (my dad found it one day and I got in major trouble). She said she had walked in on her parents having sex all the time, going down on each other, etc... that gave us plenty of inspiration.
We also conducted "sex lessons" in my 2 acres of forested backyard, inviting the neighborhood boys over to lay on the ground and squirm on top of them, fully clothed.
We were 8!! My girl friend and I made out once, too (again, age 8), though we thought it was gross about 2 milliseconds after our tongues touched.
And I discovered erotic literature in the form of the Clan of the Cave Bear books, can you believe it? My dad had the whole series, and I thought he just liked reading about neanderthals until I opened one and found bookmarks at the steamy sections. My friends and I would sit around and read those sections all the time, when the parents weren't home (up till I was 11 or 12). That was the only sexual reading material I ever found in our house, though my aunt had "The Joy of Sex" at her place and I checked it out every time she went to the bathroom!
Oh yeah, also right up until I became a Christian, I had an creepy uncle who gave me Leisure Suit Larry games from Sierra... anyone else have those? I learned about all kinds of things from that game, until my dad found out about it and I had to stop (also that whole Christian thing made me banish it all voluntarily). Talk about an adult game!! I had no idea.