Yeah, don't worry--you've got plenty of time. I didn't start costuming until I was 19 and had had a job for quite some time. Even then, I've only made one costume per year, and the latest one looks like it's going to take two years. That doesn't mean that I didn't read cosplay and steampunk websites at 12.
Another good starter sewing project is square pillows. Start with plain ones and then keep ante-ing up the decoration. You could even make them super nerdy and eventually applique on video game and anime symbols.
Then you could move up to blankets or simple clothing. Try qwik sew patterns or the easy rated vogue patterns after you have a strong handle on pillows. Simple plush animals or Christmas/holiday decorations can also be a great start after perfecting square pillow skills.