I think they had to make him 18 because the ML is a brat. Pretty sure he was shit talking her to keep the other guys away from her. Also, he lashes out at her when his feelings are hurt instead of correcting her assumptions/misunderstandings. Meanwhile, the FL is too stupid or insecure to handle him properly and put him in his place. I wish she was cooler. I'm tired of these doormat FLs.
The ML is really cute but the FL is just…so unlikeable.