immature

adjective

1 white Stilton is a very young, immature Stilton:

unripe, not ripe, not mature, not matured, unmellowed;

undeveloped, unformed, imperfect, unfinished, incomplete;

crude, raw, green.

▷antonyms ripe, mature.

2 she is an extremely shy and immature girl:

childish, babyish, infantile, juvenile, puerile, jejune, callow, green, inexperienced, unsophisticated, unworldly, naive, ingenuous;

informal wet behind the ears, born yesterday.

▷antonyms mature.

word toolkit	immature
See youthful.

immature Oxford Dictionary of English