Well shes been out with you a few times now and obviously enjoys your company, so if your ages f**ks anything up after her previous misconceptions then there's something wrong with her and you're probably better not hanging around with her. But whatever you do, don't announce your age like it's a big deal, like when a 7 year old decides to pick up a piece of fruit and parents go "OMGZ he's eating fruit!!! Call the newspapers", i can guarantee that kid won't pick up another piece of fruit for months. Normally it would be a case of 'don't bring it up it's not a big deal' but obviously it bothering you so just bring it up when the time is right, but like i said before don't say 'you know i'm X years old' like it's a bad thing, call her old jokingly one day and she'll ask you how old you are and go from there. She probably won't care and you've been worrying for no reason.