Let's sexualize the kid!
I don't know how young the girl is meant to be, but it's repeatedly alluded to that she's too young for an 18 year old boyfriend, so she's definitely supposed to be under age.
It's one thing to depict her being in a romance - that's fine. But the camera lingers lovingly on her body during scenes where she makes out with her boyfriend. It's clearly intended to invite the viewer to assess her sexual desirability. Even though the actress wasn't really that young, it's just a creepy approach.