The Collaborative International Dictionary of English v.0.48:
Boyish \Boy"ish\, a. Resembling a boy in a manners or opinions; belonging to a boy; childish; trifling; puerile. [1913 Webster] A boyish, odd conceit. --Baillie. [1913 Webster]WordNet (r) 3.0 (2006):
boyish adj 1: befitting or characteristic of a young boy; "a boyish grin"; "schoolboyish pranks" [syn: boyish, boylike, schoolboyish]