I a junior and a freshman likes me...?

So I am a 17 year old girl and a junior in high school. So my friend (a senior) and I always go to the library during study hall. I usually beat Sean there because he is usually with his girlfriend before class. The other day I took my usual spot by the chess board and pulled out my tablet to read and this guy walked over and we played a game. Sean came in not much later and I made them play each other. The kid didn't tell us his name or grade until we told him first and he seemed surprised that we were upperclassmen but neither of us were surprised because we did not recognize him and it is a small school. Sean always teases me about being single so of course he had to mention this to the kid and he made it sound like I was looking or something. Today, the kid came back and we played a couple of games while Sean was in guidance and he asked me questions about relationships and I could not tell if he was flirting or looking for guidance but he seems interested. I am not- I would rather not date a boy 2-3 years younger than myself for the mental maturity difference. Not that I haven't dated different ages- when I was 16 I dated a 19 year old and I have dated two other guys, between 6 months and a year younger, however, three years is a lot to me at the moment. I don't really know how to get this kid to u derstand that I am not intetrsted gently.