The Collaborative International Dictionary of English v.0.48:

Prematurity \Pre`ma*tu"ri*ty\, n. [Cf. F. pr['e]maturit['e].]
   The quality or state of being premature; early, or untimely,
   ripeness; as, the prematurity of genius.
   [1913 Webster]

WordNet (r) 3.0 (2006):

prematurity
    n 1: the state of being premature [syn: prematureness,
         prematurity]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "prematurity":
   forwardness, haste, hastiness, impropriety, impulse, impulsiveness,
   inappropriateness, inauspiciousness, inconvenience, inexpedience,
   infelicity, inopportuneness, inopportunity, intempestivity,
   interruption, intrusion, irrelevance, lateness, overhastiness,
   precipitation, precociousness, precocity, prematureness, rush,
   unfavorableness, unfitness, unfittingness, unfortunateness,
   unpropitiousness, unripeness, unseasonableness, unsuitability,
   untimeliness, wrongness