immature
adjective /ˌɪməˈtjʊə(r)/
  /ˌɪməˈtʃʊr/,  /ˌɪməˈtʊr/
 - behaving in a way that is not sensible and is typical of people who are much younger
- immature behaviour
 
Wordfinder- adolescent
 - immature
 - mixed up
 - naive
 - puberty
 - rebellious
 - sulky
 - tearaway
 - teenager
 - young
 
Extra ExamplesTopics Personal qualitiesb2, Life stagesb2- Although she was older than her husband, she was emotionally quite immature.
 - He displays very immature behaviour for a boy of 16, running about the classroom and yelling.
 - Oh, don't be so immature.
 
Oxford Collocations Dictionaryverbs- be
 - seem
 - sound
 - …
 
- extremely
 - fairly
 - very
 - …
 
 - not fully developed or grown
- immature plants
 - The immature birds have shorter tails and brown, speckled plumage.
 
Oxford Collocations Dictionaryverbs- be
 - seem
 - sound
 - …
 
- extremely
 - fairly
 - very
 - …
 
 opposite mature 
Word Originmid 16th cent. (in the sense ‘premature’, referring to death): from Latin immaturus ‘untimely, unripe’, from in- ‘not’ + maturus ‘ripe’.