My Sims twins were born in the game. I do agree in some way, their feature does look like YA. So, I dressed them up with cloths that it seems appropriate for their age, give them hairs to look like teenagers, although this can be tricky. Like in the earlier 'years' of my teen Sims, they are kinda chubby..
https://i.imgur.com/b1dJ50c.png?1 In their formal attire.
As the days passed, they have slimmed down and they look a lot like teenagers now.. The teen girl got so skinny, and the teen boy has a less refined body muscle... The mum is an adult. FYI, I don't use any CC or modified them in CAS except for changing their cloths and hairs
https://i.imgur.com/OerNdRI.png?1 https://i.imgur.com/gcTspjB.png?1
