How do you impress a senior girl if you are just a freshmen?

The first thing I have to say, is that a major turn-off to girls is when a younger guy is trying too hard to impress them. Now that that's out the way... you should just be yourself around the senior girl. Most girls can tell when a guy is being fake, and that's another turn-off. She'll want you to be real first - even if she doesn't like a few little things about the real you. It shouldn't matter whether you're a freshman, sophomore, junior, or senior, but if it does, you probably won't want to be with her because that means she's obsessed with what other people think of her. If she likes the real you, you've impressed her just by being yourself - and that's a lot of points on her scale.