If you just cannot wait to study at FIT, there are classes available to middle and high school students. The program is called Saturday Live (or Summer Live depending on what time of year it is). One of my friends, who is now at RISD, told me about the classes and I ended up taking five different courses while I was in high school:
Manual Patternmaking and Sewing
Introduction to Fashion Design Industry
Creative Fabric Painting
Fashion Art for Fashion Designers
Fashion Art Portfolio
The classes would run from 9-12 and then 1-4 after lunch. I lived in Westchester so I did the morning Metronorth commute with all the parents who lived in my town. The classes were good for laying down the basics for the courses I would take when I got to college. They were fun and not very stressful, so we could take risks and not worry about failing. You do get graded in these courses, but the grades do not hold any college credit value and are therefore just meant to help you evaluate yourself.
While you certainly could never replace, say, the college level patternmaking couse with the one I took over the summer, the classes were a fantastic place to meet other fashion-focused kids my age, test the waters of various disciplines and evaluate my base skill levels.
I realized that I was set on going into fashion design in college, so I took classes specifically to improve my portfolio. Taking these classes certainly does not guarantee you will get into FIT, but actually working in the classrooms with real teachers from the college helps tremendously. I think it also gives a great sneak peak into what it would actually be like to go to FIT. My Fashion Art Portfolio teacher reviewed my portfolio before I sent it in with my application and then I ended up having her as my Fashion Art & Design professor second semester! She even recognized me on the first day of class. Now, they have even organized the classes into groups so you can see which to take in preparation for certain majors.