The Collaborative International Dictionary of English v.0.48:
Immaturely \Im`ma*ture"ly\, adv. In an immature manner. --Warburion. [1913 Webster]WordNet (r) 3.0 (2006):
immaturely adv 1: in an immature manner; "his teenage son still behaves very immaturely" [syn: immaturely, jejunely] [ant: maturely]