I don't think a difference of 3 years is so important, and it's quite common to have girls going for older guys. 13 and 16? I see no problem there.

As for the temporary crush, I think you people should get real. Even for people in their twenties feelings start fragile, and then become stronger with time. And you don't intend to marry this girl, right? So why not take your chance to enjoy your time with her, and take this opportunity to mature a bit?

All in all, I think you are asking yourself too many questions. Just go for it, enjoy it. Who knows, it may even turn to be your lifetime relationship. Unlikely, but so are all relationships anyway. At the least, it could be a relationship which could provide fond memories for the rest of your life,...