juvenile

Short definition from Wiktionary

Adjective

1. 1
   Young; not fully developed.
2. 2
   Characteristic of youth or immaturity; childish.

Noun

1. 1
   A prepubescent child.
2. 2
   A person younger than the age of majority; a minor.
3. 3
   A person younger than the age of full criminal responsibility, such that the person either cannot be held criminally liable or is subject to less severe forms of punishment.
4. 4
   A publication for young adult readers.
5. 5
   An actor playing a child's role.
6. 6
   A sexually immature animal.
7. 7
   A two-year-old racehorse.