Immaturity is the state of not yet being fully developed or grown up, either physically or in behavior and thinking. A sapling shows immaturity compared to a towering oak tree. A young wolf pup displays immaturity in its clumsy hunting attempts.

When people talk about immaturity in humans, they usually mean someone acting younger than their age or the situation requires. An immature response to losing a game might be throwing the board across the room instead of congratulating the winner. Immature behavior at school might mean constantly interrupting the teacher with silly jokes when serious discussion is needed.

Everyone shows immaturity sometimes because growing up happens gradually, not all at once. A ten-year-old who whines like a toddler when asked to do homework is showing immaturity. But that same child might show surprising maturity when comforting a younger sibling who's scared.

The opposite of immaturity is maturity: the ability to think ahead, control your emotions, and respond to situations thoughtfully rather than impulsively. Physical immaturity simply means your body is still growing. Emotional or mental immaturity means your judgment and self-control are still developing. Both kinds improve naturally with time and experience.