juvenile (adj.) Look up juvenile at Dictionary.com
1620s, "young, youthful," from Latin iuvenilis "of or belonging to youth, youthful," from iuvenis "young man, one in the flower of his age" (in Roman use, the period just beyond adolescence, from age 21 or 25 to 40), noun use of an adjective meaning "young" (source also of French jeune; see young (adj.)).

Meaning "pertaining to or suited to youth" is from 1660s. As a noun, "a young person," from 1733. Juvenile delinquency first recorded 1816; Juvenile delinquent the following year. Slang shortening juvie/juvey is recorded from 1941 as "juvenile delinquent," 1967 as "juvenile detention."