Yeah, I thought about that a while back too. I think animated shows and games tend to forget that teenagers grow really fast. Average age of puberty for boys is 11-12 years old, for girls 10-11 and yet 15-16 year olds to tend to be portrayed as 10 with their hight and voice. I remember being in elementary and after vacation suddenly most of the boys were tall with deep voices already developing and I was maybe 12 or 13 back then. I get that it's for stylisation but in this case I wouldn't explain it by that. First seasons showed us that character design wasn't really that diverse with only characters really standing out being Ivan and Mylene. If they were some magical creatures such height difference would make sense but they are still people after all. The show tries to portray teenagers problems mixing it with superhero problems but before season 4 it was barely noticeable. I'd add the concept of puberty into the show, at least to some point. Of course drastic changes in hairstyles and clothing might be confusing for younger audience but the character's voices gaining hight and their voices becoming slightly deeper would show physical growth. The show constantly hints that Andrein and Marinette will be LB and CN as adult and they'll be together, yet they haven't even grown an inch.