puerile

lapsekas, lapsellinen Characteristic of, or pertaining to, a boy or boys; confer: puellile.
childish Childish; trifling; silly.
(rfdat) De Quincey:

The French have been notorious through generations for their puerile affectation of Roman forms, models, and historic precedents.

From the table he had received the gout; from the alcove a tendency to convulsions; from the grandeeship a pride so vast and puerile that he seldom heard anything that was said to him and talked to the ceiling in a perpetual monologue; from the exile, oceans of boredom, a boredom so persuasive that it was like pain,—he woke up with it and spent the day with it, and it sat by his bed all night watching his sleep.