(No offense meant by any of this post, but I'll be as direct as possible..)
Dude, you're 27 years old. At 27 years of age, you shouldn't be hanging out where high school kids hang out, you shouldn't be "hitting it off" with high schoolers, you shouldn't be dating high schoolers, and you sure as hell shouldn't be going to prom. Get a grip.
Some people will point to the 9 year age difference and say, "Well, my 41 year old uncle has a 50 year old girlfriend, and that doesn't seem so weird," you need to realize that at this stage in your life and especially in her life, it is very much weird. Once both people in a relationship have jobs and decades of life experience, the gap closes practically. The difference between a 27 year old and an 18 year old (should be) light years, assuming that you have the maturity level of a 27 year old. (Don't tell me that she has the maturity level of a 27 year old, either. She lives with her parents. She's never paid bills. Don't go there.)
That isn't healthy and it's not going to end well... but I wish you the best of luck. It was interesting to read.

.... no I would shoot ya
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