I think the issue is that twelve through nineteen is SUCH a variation between ages that its hard to pick a look that labels them as "teen". What I'm going to try and do, is sort of split their lifestage into two. So a toddler is like 2-4 and a child is about 6-8 and then 9-11. So the younger side of being a child, they would be in things their parents would pick out for them to wear and they get a slightly "older" look later (just whenever in-game I feel like they've spent enough time as one "age").
So same with teens, start them sort of as awkward 12-14 year olds with no makeup or minimal, then move them into clothing style that's more 15-17ish. I even want to implement this on my young adults and adults. I always forget to make adults that look like they're in their 40s or 50s, they seem to always been young 35 year olds. So I've moved that age into the YA lifestage.
Another thing too (sorry if this is starting to not make sense), is that I sort of pick a style for their personality and modify it in each age. But there's also those people who never grow out of dressing like a teenager.
I second a lot of things said as well with crazier hair, colors/patterns of clothes & intense make-up or none at all. Braces, acne & bad style can also help. lol
