Once again, I agree with Vashti!
I'm just going to put that in my sig...
If it's that important to you, you definitely should approach her! Don't be scared! Just work up the courage & go for it. I know all too well about dating a younger guy senior year. I just graduated & my boyfriend & I are having to break up b/c I am going away. It's painful! I don't regret dating & falling for him, but it has made my transitions much more difficult! It will be good practice for you though if nothing else.