I recently posted a thread about the crush I've developed for my hot ass boss. It would be less tempting I think if it wasn't even in the realm of possibility. But the fact that, on our side at least, extra-marital adventures are not off the menu, it makes it that much harder to just put it from my mind. So I can empathize with your struggle here, LOL.
As I mentioned there, I personally don't have an issue with playing with a coworker - or even my boss, for that matter - as long as everything was on the up and up, and I could be sure they could keep their shit together. I am 100% certain of my ability to keep a poker face at work, not panic at any insinuations by office mates, and know where the lines are drawn about hanky-panky around the office. Work and play would need to be totally compartmentalized, and my coworker/boss/whomever would need to understand that be able to keep up. If there were any doubt, I wouldn't do it, period.
It may not be a popular stance, but the coworker's age is a bit of a red flag for me. It would depend on the person, as some 22-year-olds are more mature than others. But the simple truth is, they don't have the same life experience of someone even 10 years older. By that, I just mean that a 22-year-old is potentially a higher drama risk than someone who's been around the block a time or two. Your mileage may vary, of course.