The Collaborative International Dictionary of English v.0.48:

Puerility \Pu`er*il"i*ty\, n.; pl. Puerilities. [L.
   puerilitas: cf. F. pu['e]rilit['e].]
   1. The quality of being puerile; childishness; puerileness.
      --Sir T. Browne.
      [1913 Webster]

   2. That which is puerile or childish; especially, an
      expression which is flat, insipid, or silly.
      [1913 Webster]

WordNet (r) 3.0 (2006):

puerility
    n 1: the state of a child between infancy and adolescence [syn:
         childhood, puerility]
    2: a property characteristic of a child [syn: childishness,
       puerility]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "puerility":
   babyishness, boylikeness, callowness, childishness, childlikeness,
   girlishness, immaturity, imprudence, inadvisability, inattention,
   inconsideration, indiscreetness, indiscretion, inexpedience,
   infantilism, injudiciousness, irrationality, maidenliness,
   pompousness, puerilism, reasonlessness, recklessness,
   senselessness, stuffiness, thoughtlessness, unintelligence,
   unreason, unreasonableness, unsensibleness, unsoundness,
   unthoughtfulness, unwisdom, unwiseness, witlessness



Bouvier's Law Dictionary, Revised 6th Ed (1856):

PUERILITY, civil law. This commenced at the age of seven years, the end of
the age of infancy, and lasted till the age of puberty, (q.v.) that is, in
females till the accomplishment of twelve years, and in males, till the age
of fourteen years fully accomplished. Ayl. Pand. 63.
     2. The ancient Roman lawyers divided puerility into proximus infantiae,
as it approached infancy, and into proximus pubertati, as it became nearer
to puberty. 6 Toullier, n. 100.