His teachers have complained about his 'immature' behavior.
The flock included both adult and 'immature' birds.
The fruit was still 'immature'. [='unripe']
(..) - Are we there yet? - We are not! - Are we there yet? - No! Are we there yet? That's not funny. That's really immature. This is why nobody likes ogres. Your loss! - I'm gonna just stop talking. - Finally! This is taking forever, Shrek. (..)2004 Shrek 2