Just play it off and plow through it. Have to emphasize she looks younger than 29 (when I first saw you I thought you were 23 but I wasn't going to say anything or ask how old you were) and you look older than 19, and the key thing is that you get along well. Emphasize that you're both in your sexual prime, state it as fact, and throw an Ashton/Demi reference somewhere.
It might have been the initial shock mixed with attraction the first time around.
I agree that you shouldn't ask permission to kiss her, and just wait until you feel the moment is there to do it. There's a way to work your way towards a k-close if you think she's going to turn her face. | 
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