adjective (a)

• characteristic of a lack of maturity(adj.all)

  Example:
  Immature behavior.
  

  source: wordnet30
• (used of living things especially persons) in an early period of life or development or growth(adj.all)

  Synonym:
  young
  Antonym:
  old
  

  source: wordnet30
• not fully developed or mature; not ripe(adj.all)

  Synonym:
  green, unripe, unripened
  Antonym:
  mature, ripe
  

  source: wordnet30
• not yet mature(adj.all)

  Antonym:
  mature
  

  source: wordnet30
• (of birds) not yet having developed feathers(adj.all)

  Synonym:
  unfledged
  Antonym:
  fledged, mature
  

  source: wordnet30
• Not mature; unripe; not arrived at perfection of full development; crude; unfinished; as, immature fruit; immature character; immature plans.(adjective)

  source: webster1913