Maybe you give out a very mature and sophisticated impression to people, and guys your own age thing 'oh she's out of my league' or some stupid sentiment like that, and feel they can't approach you because you have lots of men sniffing round you already, and they are much older and more experienced etc etc.
Perhaps you could try acting in a more approachable way, do you think you are mature? You are only 16, sorry to sound condescending, (don't worry I'm ONLY 18 anyways I'm hardly the highest authority) and if you want guys to be interested in you your own age you need to be approachable on their level, one which is generally more immature than most girls there age, but particularly as you are particularly mature. That's just the feeling I get anyway.
Hope that helps.