I try to limit some of the clothes. So things that are more casual or "kiddish" if you have Parenthood, that's what I have teens wear. I also find that layering clothes in fun ways with fun colors can do wonders to age a sim down, like tights and leggings in contrasting colors to skirts or shorts. It helps to dress sims for their personality, too. Not all teens are into fashion and makeup, so I really try to think about that when I make them over. Even when I have sims that would be, I still try to limit some of the clothing and makeup to YA and up, not to shame teens who do that IRL, but because I feel like the teens/YA/Adults in my game tend to look very similar otherwise. The braided pigtails style will do wonders too, if you have that one--can't remember if it's basegame or outdoor retreat.
