Go up to him and say hi I'm blah blah I'm 18, I think your cute, I like running up walls and playing light-saber dodging, how are you? Don't catch him in a hurry though, he'll think your weird and run away. But if he is relaxed and siting he will try to talk it about, but he'll probably be a little off-guard so you might want to say, you think about what to say and I'll write down this important thing.