I have had a "dwarf syndrom" happen a couple of times on the day a townie child was to age up to a teen in the evening. They would come to look like a teen prematurely in the morning, and remain in a child's body frame until evening, giving them shortened arms and legs and a teen head/face. I solved it by triggering age transition immediately.
With "grown body", I mean they simply appear to be a young adult. There is nothing abnormal about the appearance. They just look like YAs who are attending school. NRaas->Status->Personal maintains they are still a teenager - some of them even have several days left until their YA birthday. The last sim it happened to was a guy, but I forget what he wore. Pretty sure it wasn't the outfit with the little neck scarf though
I use custom skin and eyes, but not clothes whatsoever. I was adamant about not using SP, but I'm trying now anyway to see if it will fix anything. I have attempted to configure it, so that it basically won't do anything other than let sims advance in their careers and retire when old, because I don't want my town to switch partners and start to have more kids. I hope it works, but I do make it a seperate save just in case.
Thanks for trying to help! I hope I elaborated okay.