My advice would be to make sure that you've actually got something going on between her and you before you make a move otherwise it'll be a really awkward situation.
Please Be very careful what you do you don't want to ruin your relationship
It's normal for young girls for wear skinny leg jeans and a tight top that shows the bra and cleavage?? That isn't exactly cracking on to you. That's my general outfit if I'm not dressing up and going out?
If she wanted your cock she will just go ahead and grab it but What you should do is go on some dates with some nice young ladies and try to get them into your bed instead.