Immature; childish. See Synonyms at young.(adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "puerile" in a sentence
"Maitland in his _Account of the Early Printed Books at Lambeth_, 1843, already takes occasion to animadvert on what he terms the puerile competition for rarities, which had then set in."
"Your example of email being maligned as puerile is just a case in point."
"I view Goodling's use of the word as an attempt to deny responsibility for her actions by seeing herself in puerile terms."