So the first story I ever wrote was, though it shames me to say it, a fanfiction.
I couldn't have been very old, but I had decided to set out and write a satisfactory sequel story to one of my favorite videogames, one called Chrono Trigger. I don't know how familiar you might be with that old SNES RPG, but if you happen to run across it on an emulator anywhere, just go ahead and give it a try. The graphics aren't anything special, but the storyline and game mechanics still set it apart as a classic in my mind.
In any case, I decided that in spite of rumors floating around about a crappy sequel already in the works, I could write a decent story on my own. My theory was that after the big bad of the first game was destroyed, others of its ilk would come and try to destroy the world in the far future, which Chrono and his friends would then need to prevent. To do so would require that each of them increase their skills, resolve some personal issues and confront these new invaders to guarantee the survival of the world.
It was a wonderful little story that eventually contributed to my later development of the Game. (In Chrono Trigger there are only four elements, but I decided that the characters who didn't use magic or duplicated elements deserved to each have their own. Thus I ended up with the Seven Elements that the Game used from then on.) I had a wonderful time working on it, though my skills were obviously limited and the plot was a little Mary Sue-ish. At the same time, I felt the first little sparks of excitement over the chance to develop and create a story all my own.
Unfortunately my first foray into the world of words came to an abrupt crashing halt. My manuscript disappeared when I was about three dozen pages in or so, and I had not learned to back things up in any significant way. With that, my first attempt was crushed before I even completed a first draft, and I drifted away from the project afterwards.
At least, until my second attempt a couple of years later...