Responses
I think you answered your own question tbh, the flow of the story is too mature for the age setting so the character design is doing a lot of the heavy lifting.
To be honest, when I was 15/16 almost 11 years ago, I looked like like full blown adult. Nobody believed me when I told my age. And also I think, making child like characters in a love story would be a littlebit off limit even knowing their age…
Okay why are they drawn as adult when they are supposed to be 15/16 first years of high school. At this point the author should have made them first years in college with a past in middle school and high school. They look and act too old making be forget their age.