juvenilely

This adverb carries a strong negative connotation, typically describing behavior that is inappropriately childish for a person's actual age. It suggests a lack of emotional maturity or a failure to adhere to the social expectations of adulthood, often implying a sense of irritation or judgment from the observer.

Because it is a derivative of the adjective "juvenile," it is used less frequently in spoken English than phrases like "childishly" or "in a childish way." It is more common in written reports, psychological evaluations, or formal critiques of behavior where a precise, clinical tone is desired.