Nubile refers to a young woman who is ready or suitable for marriage by virtue of her age or maturity. Since at least 1973, it has also been used to refer to a sexually attractive young woman.
The English word traces its roots to 1642 in reference to being "marriageable" (as said of a woman) from the French nubile. Its historical roots, though, can be traced still further back to the Latin nubilis, also meaning "marriageable," which is from the stem of nubere which means "take as husband".
In 1973 it was first used in the sense of "sexually attractive." The word can refer to a nymphet (see below) in the context of a young sexually attractive woman.
A nymphet is a sexually attractive girl, or young woman. The first recorded use of the term, defined by The Century Dictionary as "a little nymph", was by Michael Drayton in Poly-Olbion I. xi. Argt. 171 (1612): "Of the nymphets sporting there In Wyrrall, and in Delamere."
In Lolita, "nymphet" was used to describe the 9- to 14-year-old girls to whom the protagonist is attracted, the archetypal nymphet being the character of Dolores Haze. Nabokov, in the voice of his narrator Humbert, first describes these nymphets in the following passage:
Plot
Clyde Calloway was faced with the decision of last resort. The choice he made led him into a sordid world of desperate souls, dirty money, and deep secrets. Now -- his last day on the job, his last day before becoming a free man -- everything he chose to leave behind is about to catch up.
Never believe in the hopeless case