Also, sometimes an adult wants to dress like a teen, maybe they can pull it off but when not, let 'em fail, it's a personal choice.
And I want to reiterate, whether teens are shorter, taller, or equal to "adults" (many, randomly assorted adults) is not really as much the question as, "are teens their own full height?" Usually YES. Especially girls 14+ (14!!!!) but many boys too, if not most, depending on which years we count.
In the game the "teen" years are actually just high school years, so they might "start at" 14/15 and end at/by 18. TS4 mentions high school, which I don't think was a vanilla ts3 thing, at least based on The One school building.
I would love pre-teens though, and middle-schoolers / junior high ... ers? ... jr. high kids. Heh heh. :)