Can a traumatic event be enough to stunt your mental growth?

Anonymous
We're worried about my cousin's lack of interest in dating, finding another job (he got fired recently for slow performance), his lack of knowledge in how to pay bills, run a house, etc. It's been years already and it seems like he's stuck in time. Many of his manners and the way he talks about videogames, love, etc sounds like a HS teenager, not a grown 22 year-old man.

The event that's deeply seared within him
He was 16 at the time (his then girlfriend was the same age), it was his first and they were dating for 6 months or so. He had just gotten his very first driver's license (restricted though) at the time. The 3rd time he drove, a drunk driver hit them, injuring him and killing his girlfriend. Though it was said she was briefly alive for a few minutes and died in his arms.

He hasn't been acting his age since. What do you think? Can a normal person's mental growth get stunt so much after a traumatic event? At the time he was acting his age but now he's not.
Yes
No
Select gender and age to cast your vote:
Updates
1 y
Several of my friends and people in the family have commented the same; that he acts and sounds like a 14-16 year-old.. as if he's stuck back in time.
Can a traumatic event be enough to stunt your mental growth?
3 Opinion