puerile

"Puerile" may call to brain qualities of childhood and childishness, other than the word itself is no coil rooster. On the contrary, it's been around for more than three centuries, and its predecessor in French and Latin, the adjectives "puéril" and "puerilis," respectively, are far older. Those two terms have the same basic meaning as the English word "puerile," and they both trace to the Latin noun "puer," meaning "boy" or "child." Nowadays, "puerile" can describe the acts or utterances of an actual child, but it more often refers (usually with marked disapproval) to occurrences of childishness where adult maturity would be expected or preferred.