As a young boy (7, 8, something) there was a store in the Mall near where I lived with all kinds of fanasy stuff. I remember seeing lots of pewter minis, fantasy magazines and stuff. Never bought anything there though. I was a big fan of He-Man so this was right up my alley.
Durring my first year in Middle School, I had a very boring Social Studies class and durring our spare time I talked with another kid in there. One day he brought in a D&D player's manual and we played in class. He DMed, I played. Looking back on it he did such a simplistic, horrible job but at the time it was totally a new experience to me and I loved it.
So we started playing a lot more (mostly OUT of class, hehehe). I met some other kids who lived near me and an Uncle had left some D&D books at their house. So, I saw the DMG and MM for the first time. I read through them, and started DMing for everyone. I never had a "real" DM to learn from, so like most people here I learned with a lot of trial-and-error and creative thinking.
Since then I've almost always been the DM, and one of my players is still that same kid who I met all those years ago in a boring Social Studies class. We're in our early 20s now.