puerile

This term carries a strong negative connotation, suggesting a lack of maturity that is inappropriate for the speaker's actual age. It describes behavior that is not merely youthful, but irritatingly juvenile or simplistic, often used to criticize someone's lack of sophistication or seriousness. In professional or academic settings, the word functions as a sharp critique of intellectual laziness or an inability to engage in adult discourse. It differs from "childish" by implying a more deliberate or stubborn adherence to triviality.