callow adj.

Middle English calwe, Old English calu "bare, bald," from Proto-Germanic *kalwa- (source also of Middle Dutch calu, Dutch kaal, Old High German kalo, German Kahl), from PIE root *gal- (1) "bald, naked" (source also of Russian golyi "smooth, bald"). From young birds with no feathers, the meaning was extended to any young inexperienced thing or creature, hence "youthful, juvenile, immature" (1570s). It is apparently not related to Latin calvus "bald."