immature

1 being in the early stage of life, growth, or development immature frogs are called “tadpoles” Synonyms adolescent, young, juvenile, 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 an immature teenager who still threw tantrums Synonyms adolescent, babyish, childish, infantile, jejune, juvenile, 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 many high school students are still too immature to foresee the consequences of their actions Synonyms adolescent, green, callow, inexperienced, juvenile, 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