man child

noun2

1. •
   (informal) An adult male who is childish or immature.

   • In the end, Brown said he just couldn't stand another day of trying to run a team with two sets of rules — one for 11 players and the other for the man-child superstar. — 2004
2. •
   (no longer used) A young male human; a boy.

   • Bring forth Men-Children onely: / For thy vndaunted Mettle should compose / Nothing but Males. — 1606