El Stud, this might be the best post you have ever made. I'm not trying to be a d!ck, and I'm sorry if I come off sounding like that, but you are actually demonstrating some game here and a decent amount of it at that.
Let me break down what is happening here.
You have social value over this chick because you are a senior and she is a freshman. That is the wonderful thing about high school, the upperclassmen - even the freaks and geeks - have instant social value because of their age. All the while, you are ignoring her and telling her she can't have you, which is just raising her IL even more for you. This is a classic demonstration of girls wanting what they can't have.
I'd imagine that you bringing up the age difference is helping your cause even more and only working to increase your social value.
What would I do if were you? I'd hook up with her, and I hope I don't sound like a complete perv for making that suggestion. Here's why. Tons of my friends in high school dated freshmen when we were seniors and nothing ever came of it, even though they were having sex. At the very least, just go out with her a little bit and get some experience with her before you head off to college. You can't get arrested or in trouble for making out with her I don't think.
You don't want to be that guy living on the dorm room floor who wouldn't know a pu$$y if one was put on his nose. Every guy on this message board who went to college I'm sure can identify a guy they knew who came into college as a freshman without ever having any sexual experience with girls.
At least think about it El Stud. I think it would really help you out if you got a little action and experienced some success - even if it is just making out. This girl wants your bones. Just invite her out to a party or for a date even and kiss close her. Shouldn't be hard, as it sounds like she is already hot to trot.