1. I started GM'ing in the early 80's in ADnD so I guess about 25 years or so.
2. I had really enjoyed playing when I was in college. After I left college, I had friends I worked with who were interested in learning to play and since I was the only with experience, I had to become the DM.
3. I had a good example in the guy who had run the games in college. I usually use the pre-built modules and then modify them a little as needed so I didn't have quite the learning curve that I would have if I needed to design the whole campaign from scratch.
4. My players have always said they think I do a very good job. I feel I could do better than I do if I could make the time to really learn the module well before hand but I seldom have the time to do that. I would still like to design a campaign myself from scratch sometime. I have a group I play with now that would probably be open to that... One of these days!
5. I enjoy playing and DM'ing. I would prefer if I could get into a situation where myself and another DM alternated playing and running the game on alternate weeks. I think that would be perfect!
Incidently, I have played other games... Morrow Project, Gamma World (a little) and a few others but still prefer ADnD, 1st edition although I'm finding as I learn more about the newer versions, I tend to selectively add bits and pieces from the newer rules.
You know your stuff. I'm not good at being a game master but I think I make a good player. At least I made it out of the last scenario alive. Join us in medieval because we'll need as many as we can get for the wolves.