I didn't have any special interests until I was 15 years old. My step father tossed a book the size of a dictionary on my lap and said "Because I can't imagine you playing video games all your life..." It was Mastering Visual Basic 6, Now I program computers in multiple programming languages and in my spare time I enjoy programming my own custom video games xD ironic no?
You might already have a special interest, It's what you talk about all the time, it might be simple or it might be simply part of something nobody can understand.. For instance you could like trains, or alternatively you could be fascinated how a steam train's engine works and you only care for steam engines.
Even if you haven't found that special interest yet, you will definantly know when you find yours. It will be something that just clicks, you will read about it nonstop and know everything about it, how it was, how it came to be, where it's headed, who invented it, what year, time, date. Why it was created, to what purpose it's used and planned for use. etc. Most likely you won't be able to shut up about it either xD