I'm going to have to disagree with every point the op made. You say if you look at their body shape and faces they look younger this is just not true overall the community disagrees with you, we had people sending Guru's images of their teens that looked like older adults and others wondering why their Sim could not flirt with another Sim which was actually a teen it came to the point we needed a name plate to say teen to notice the difference.
Now you say "they're a head shorter till 21" how so we were given a young adult life stage 18 is a young adult who starts University I have yet to play a Sim a head shorter in University
You also say "Most 15 or 16 year old boys IRL are as tall as their fathers" why should we only play such a small portion of a teens life when many of the teen years are spent as an adult 18-19 as you say and I really have not seen many 15 year old as tall as their fathers some may be many are not and still have growing to do.
You also mentioned people think 11 year old as teen I have yet to see this one sure many want preteens and find it very weird to have a Sim go instantly from a small child playing with toys to a fully grown man-teen besides the complete weirdness of it the many story telling possibilities are just not there with such a huge jump in time.
