big boy

noun4

1. •
   A large object or person.

   • I've been dying to get behind the wheel of this big boy.
2. •
   (informal) A male child who is considered mature enough for some purpose.

   • You're a big boy now, and big boys go to school.
3. •
   (informal) An adult male, considered to be sufficiently mature and independent.

   • He is a big boy and can take care of himself.
4. •
   [usually plural] One who is in a dominant position, such as in business, elite sport, etc.

   • He started a small manufacturing plant, but he couldn't compete with the big boys.