juvenile

1 being in the early stage of life, growth, or development a juvenile alligator just hatched from its egg Synonyms adolescent, immature, young, youngish, youthfulRelated Words ephebic, minor, preteen, subadult, teenage (or teenaged), underage; embryonic, emergent; callow, green, inexperienced, puerile, raw; babyish, childish, childlike, infantile, infantine, kiddish; undeveloped, unfinished, unfledged, unformed, unripe, unripened; blooming, blossoming, burgeoning, flourishing, floweringNear Antonyms aged, aging (or ageing), ancient, elderly, geriatric, long-lived, old, older, oldish, senescent, senior; full-blown, full-fledged; golden, mellow, ripe, ripened; middle-aged; anile, decrepit, doddering, over-the-hill, senile, spavined, totteryAntonyms adult, grown-up, mature, matured

2 having or showing the annoying qualities (as silliness) associated with children throwing a tantrum is rather juvenile behavior for a person of your age Synonyms adolescent, babyish, immature, infantile, jejune, childish, kiddish, puerileRelated Words boyish, brattish, bratty, girlie (or girly), girlish; childlike, innocent, naive (or naïve), simple, simplistic, unsophisticatedNear Antonyms unchildlike; cosmopolitan, experienced, knowing, smart, sophisticated, worldly, worldly-wiseAntonyms adult, grown-up, mature

3 lacking in adult experience or maturity a spoiled, juvenile golfer who does not know how to win gracefully Synonyms adolescent, green, immature, inexperienced, callow, puerile, raw, unfledged, unformed, unripe, unripenedRelated Words babyish, childish, infantile, infantilized, infantine; boyish, girlish, juvenescent, kiddish, young, youngish, youthful; maidenly, virginal; ingenuous, innocent, naive (or naïve), tender; unknowing, unseasoned, unsophisticated, untrained, untriedNear Antonyms advanced, precocious; knowing, savvy, sophisticated, worldly, worldly-wiseAntonyms adult, experienced, grown-up, mature, ripe