The first fandom I was ever involved with was Duran Duran, starting when I was about 12 years old (1982). Looking back, I'm interested by how different it was from the fandoms with which I've interacted more recently, because my first fandom experience took place long long ago, in a galaxy far far away ... in which there was no Internet. Yes, I know it's shocking, but I really am that old.
Since there was no Internet, my so-called involvement in Duran Duran fandom consisted entirely of sitting around with my friends and squealing over the newest videos, collecting everything I could get my hands on, and exchanging letters (remember those?) with about a dozen different "Duranie" pen pals in the U.S. and U.K.
I wrote Mary Sue fics (though I didn't know that's what they were), but I don't think anyone else ever saw them, because there was no easy method -- such as there is now -- for embarrassing myself on a global scale.
I wore Duran Duran t-shirts to school every single day, like a complete dork. I got my hair cut like one of the members of the band. Basically, I was a true fanatic. But a very isolated fanatic, because there wasn't much opportunity to connect with other fans.
It wasn't until about 20 years later that I got involved in another fandom. In the meantime, I had a sort of brush with science-fiction fandom, just because several close friends were involved there. I also had a sort of brush with gaming fandom, because two boyfriends (one of whom eventually became my husband) were involved there and due to that connection I played an online game for almost a year.
But my own second real involvement with fandom didn't happen until I got involved with the online Buffy fan community a couple years ago. It's like a completely different experience, because everyone is so closely connected to each other. But, oddly enough, I've found that the things I like most about the Buffy fandom were the same things I liked about the Duran Duran fandom: connecting with individual people. I now get to know people through LiveJournal and/or emails -- instead of through paper letters -- but the result is the same: connection with people who understand and share an interest.
I'm not much involved in Buffy fandom anymore. I started pulling away because of the frequently argumentative politics. This fan attitude is good, but that one is bad or This character is good, but that one is bad or This interpretation is right, and that one is wrong. The whole thing pisses me off.
But I'm still glad for the people I've met and the friends I've made. I hope some will last beyond the fandom.