Im Dal-Young must have been under contract to produce an ending or something like that. Usually he just leaves things unfinished once he runs out of half-baked ideas.
Technically there are different names for different age brackets, but it's tricky to even say that without sounding like you're defending it...
But yeah, 15? Big oof.Specially since the father takes advantage of it when hyping up her physical apparence to get him onboard. And for no reason at that, since all it accomplishes is putting contrived expectactions on the otherwise well natured guy.