His teachers have complained about his 'immature' behavior.
The flock included both adult and 'immature' birds.
The fruit was still 'immature'. [='unripe']
(..) or the weird-looking Hilton sister? She looks like exactly the kind of gold digger... who would latch onto an immature little con artist like Jason. My goodness, Emily, tell us how you really feel about the boy. But when you say "gold digger," do you mean she was cheap-looking? - Yes. (..)2004 TvShow: Gilmore Girls Title: The Nanny and the Professor Season: 4 Episode 10