WordNet sense 1 (not having feathers):

unfeathered

WordNet sense 2 ((of birds) not yet having developed feathers):

immature

WordNet sense 3 ((of an arrow) not equipped with feathers):

fledgeless, unvaned

WordNet sense 4 (having no feathers):

featherless

WordNet sense 5 (young and inexperienced):

callow, fledgling

WordNet sense 6 (lacking practical experience or training):

inexperienced, inexperient