immature

characteristic of a lack of maturity

• “immature behavior”

lacking in development

• “immature plans”
• “an unformed character”

(used of living things especially persons) in an early period of life or development or growth

• “young people”

not fully developed or mature; not ripe

• “unripe fruit”
• “fried green tomatoes”
• “green wood”

not yet mature

(of birds) not yet having developed feathers

• “a small unfledged sparrow on the window sill”