If she had met him when he was 18 and out of high school, that would be one thing. Marvel was doing this when he was 16 and it was illegal.
Yes, I do have a personal hang up over relationships where the minor crushed on the legal adult and the adults response was "Not yet". If the adult let this kiss continue in public she would be contributing to the delinquency of a minor, possibly be jailed up to one year, and fined. She didn't but that's not really the point. She continued touching him, laying her head over his shoulder in a manner intended to be romantic to the readers. Instead, her response should have been "Dude, you're a literal kid, no." It's fine for him to have a crush but since they decided to be creeps and have her reciprocate, the writers can wait until he is 20 before getting them into a relationship. These two are fictional ink creations incapable of feeling anything without creators plotting it out. I'm sure they'll survive.