juvenile

(noun) a young person, not fully developed. Synonyms: juvenile person.

(adj) of or relating to or characteristic of or appropriate for children or young people. Examples: "Juvenile diabetes." "Juvenile fashions."

(adj) displaying or suggesting a lack of maturity. Synonyms: adolescent, jejune, puerile. Examples: "Adolescent insecurity." "Jejune responses to our problems." "Their behavior was juvenile." "Puerile jokes."