I can tell teens apart from young adults easily, as teens their faces are rounder and they are a lot skinnier then older sims. The older the sim gets the more they fill out and start to hunch. Adults sims start to get eye bags and a few wrinkles.
But i do dress my teens as well teens, depending on personality and story. For example I never put heavy make up on my teen girls, and they never wear heels unless it formal. I also dress them in baggy, torn clothing, layers, and some times short shirts for the girls. Their hair is either messy, hanging in eyes, pulled back, or up.
Here are some of my teen boys
Baggy Shirts, pants, layers, hair that is either messy or covering eyes.
https://i.imgur.com/K42nQDL.png
https://i.imgur.com/IY3S3uZ.png
Teen girls
style ranges from either preppy or athletic
https://i.imgur.com/vRCxMu9.png
https://i.imgur.com/lfQqPmZ.png
