If you're into mods, I think there's a mod out there that adds a height slider to CAS so you can make your teens shorter.
As for just regular CAS stuff, I use braces and acne to differentiate most of the time. If my adults are out of the young adult life stage, I use more worry lines and crow's feet skin details to add to that older look.
My older females tend to have shorter hair than my teen females. As for males, since I'm not too good at making males in CAS, I really rely on the braces and acne, mainly because I like my males to be fresh & clean haha (but some of them have bad skin and can't help it haha). I also use more teen oriented clothing from Parenthood and the letterman jacket on my athletic teen sims. Sometimes, I go with a private school feel and make one of their everyday outfits a uniform, so that also helps.
