immature in WordNet English dictionary

1. not fully developed or mature; not ripe
   "unripe fruit"; "fried green tomatoes"; "green wood"
   green  unripe  unripened  immature 
   
2. not yet mature
   immature 
   
3. characteristic of a lack of maturity
   "immature behavior"
   immature 
   
4. (used of living things especially persons) in an early period of life or development or growth
   "young people"
   young  immature 
   
5. (of birds) not yet having developed feathers
   "a small unfledged sparrow on the window sill"
   unfledged  immature