Then you should take her out and get to know each other better. There is no problem in you two dating as long as you respect each other and be responsible, as relationships are all about being responsible.
Those three years may not seem like a big deal, but the mind can change a lot in that time. Ask yourself what it is about her you like so much. Do you guys have a lot in common? Is she into the same things as you? Are you cool with her friends? Before you actually decide to date and become exclusive, I reccomend spending some quality time with her and getting to know her for who she really is. If you guys can talk easily with each other in person, and enjoy doing the same things together, then maybe you can give it a shot. Just be cautious, she's a junior, that means she'll be turning 17 this year. If she meets someone older and "better" than you, and tosses you aside, then you could easily get hurt. Just be careful.