The Oxford Thesaurus An A-Z Dictionary of Synonyms - immatureadj.

1) premature, undeveloped, unripe, rudimentary, half-grown, unformed, unfledged, fledgling, unfinished, young, new, fresh, incomplete: The immature growth in the spring is not hardy enough to survive a frost. 2) green, callow, unsophisticated, na‹ve, jejune, inexperienced, babyish, childish, childlike, puerile, juvenile, raw, Colloq wet behind the ears: She is a bit immature to assume so many responsibilities.