Well, I turn 20 in 3 months...doubt I'll change much until then.
13- Really standoffish. Mainly to impress girls, but really I was too shy and nice to really hurt anyone. It helped that over half the school was apparantly terrified of me since I wore all black and listened to heavy metal. I was awkward at "dating" and didn't really bother with it until about 2 years later.
16- Thought I was desperately in love. While I'm sure I was in love for some time, we grew bored, virginity lost and all. I was still kind of standoffish, but really I was just standing my ground as my own person at that point, not really in the mood for peoples crap and usually brooding. I was obsessed with writing in school, so I failed my first year of high school since I would rather write stories than waste time with stuff I already knew. It was also around this time that I realized how smart I was, and tried to become more social because of it. I learned that people really, REALLY don't like to be told their wrong, even if they are.
18- Still in high school, bad grades, but stopped writing. I was always told that just writing wouldn't get me anywhere in life, so I stopped that too. Lost a lot of "friends" either through responsibilities, stupid immature reasons, or they had no interest in me. Began playing A LOT of video games at one time. I decided to get 100% into PC gaming since I was learning about it over the last 5 years.
Present- Fully graduated thanks to an alternative school where I could work at my own pace. Finished 1 1/2 years of school in 3 months. Now searching for a job, about to move into a new house (still living with parent), and I have a new girlfriend that's younger, but the most mature teenager I've met. I plan on writing for about a year while saving cash, publishing a book, and trying for college or a technical school. Still gaming a lot, mainly with PC, and I have a small ring of very close friends. I'm a little overweight, so I'll be exercising soon, and that's really all about it.
Honestly, aside from getting more intelligent and learning a few life lessons, I don't think I've changed much. I'm still kind of brooding, a bit antisocial, and rather lazy. (working on that last one)