facts of life vs sex

facts of life and sex both are nouns.

Word	Noun	Adjective	Verb	Adverb
facts of life	Yes	No	No	No
sex	Yes	No	Yes	No

As nouns, sex is a hypernym of facts of life; that is, sex is a word with a broader meaning than facts of life:

Other hypernyms of facts of life include sex activity, sexual activity, sexual practice.

facts of life (noun)	sex (noun)
the sexual activity of conceiving and bearing offspring	activities associated with sexual intercourse
	the properties that distinguish organisms on the basis of their reproductive roles
	all of the feelings resulting from the urge to gratify sexual impulses
	either of the two categories (male or female) into which most organisms are divided

facts of life (verb)	sex (verb)
	tell the sex (of young chickens)
	to evoke sexual feelings