His teachers have complained about his 'immature' behavior.
The flock included both adult and 'immature' birds.
The fruit was still 'immature'. [='unripe']
(..) could be in jeopardy. Or worse, their marriage. Their marriage? So, the bad guys are trying to wreck Mom and Dad's marriage. Forget it. You're so immature. - I'm gonna go look around. - Mom said to stay hidden. I'm not gonna leave the cave. Sheesh. Cool! Cool! (..)2004 The Incredibles