sophomoric

Example:His immature acts of rebellion were causing a lot of trouble.

Definition:lacking in maturity; immature; not yet fully formed or developed; not wise or sensible, especially in behavior or speech; childlike

Example:She treated the situation with a childish response that added to the chaos.

Definition:appropriate to or characteristic of a child, especially by being silly, unreasonable, or provocative

Example:His juvenile pranks were starting to annoy the neighbors.

Definition:of or relating to children or childhood; young and inexperienced; a term used to describe behavior that is immature or inappropriate for a person's age, sometimes in a negative way