Nothing. What you’re doing is just fine. If he asks you a pointed question, then give him a pointed answer. Until and unless he does that, let him have the fantasy that you could be his girl someday. And try to enjoy the attention. One day you’ll be old and it’ll stop and you’ll miss it. If you start pushing boys away now, you’ll only accelerate that day.
He’s not going to be suddenly pushed onto the path of ultimate masculinity if you reject his amorous affections. He’ll just be sad, and really no better or worse off than before. Your feelings are not leading you astray here.