Ahhhh the usual chick shaming tactics, all laid out in a nice list (Courtsey syed):
*You know it's wrong. Don't do it.
* A guy your age getting with a girl her age...you're going to have very little in common.
*Banging this girl is only going to lead to bad things.
*At the very least, if you bang this girl it's the equivalent of admitting to yourself that you can't get girls your own age.
Other risks that apply to sex in general:
Other negatives: possible pregnancy (do you want to be stuck the rest of your life with someone you have nothing in common with...and worse, a self-admitted slut?), possible STDs, someone getting attached to the other person (not good because you guys should not realistically be dating). I'm not saying any of that's guaranteed, but even the mere possibility makes it not worth it IMO.
Now, finally lets denigrate you into an animal. I mean shiit, all men are animals, right?
It's great that she's into you, but that doesn't mean you have to be an animal and automatically hit it regardless of the consequences. Your conscience is telling you it's wrong.
Hit it man. Hard and fast, just remmeber with these sluts, glazed donut, not boston cream. Keep the filling on the outside.