Nubile is a word for young women who are attractive and "suitable for marriage" (which honestly sounds sort of chauvinistic). Feminist idealism aside, nubile is a flattering term for a gal. It means youthful and sexy.
Nubile stems from an ancient Latin term which meant "marriageable." While nice young men are certainly marriageable, the term is solely used in relation to women, and now refers to their ripe sexy beauty, not necessarily qualities that could make them a dependable, loving wife. Nubile is used more now in describing a gal who is hot and sexy — more ideal for the hip-hop video shoot, not co-hosting your family for Thanksgiving.