Grown man/woman poser
Someone who's a fragile child not just on the surface, but down to their very core.
The boy/girl was a grown man/woman poser, posing as more adult and grown up than everybody else in their environment.
Grown man/woman poser
Someone who's an adult on the surface, and a fragile child on the inside, easily hurt.
The grown man/woman poser was gonna keep acting tough until he/she figured a few things out about himself/herself.