Is two years an acceptable age gap in a relationship (details within)?

I am nineteen, a freshman in college. She is seventeen, a junior in high school. We work together and unbeknownst to me she has had a crush on me. All the other girls that work there have been dropping hints like grade school girls, "I know someone that likes you..." and so forth. Me, being the unsociable coward that I am, did nothing about this. However, she has now asked me out on a date. It feels weird that I would be dating a junior in high school, but is it?

P.S. Please do not give me any answers such as, "Do what feels right." or "Follow your heart." Just be straight with me, is this unusual or unacceptable?

P.P.S. The exact age gap is a year and six months, which sounds less weird to me. Maybe I'm worried about nothing.