second childhood vs years

second childhood and years both are nouns.

Word	Noun	Adjective	Verb	Adverb
second childhood	Yes	No	No	No
years	Yes	No	No	No

As nouns, years is a hypernym of second childhood; that is, years is a word with a broader meaning than second childhood:

second childhood: mental infirmity as a consequence of old age; sometimes shown by foolish infatuations
years: a late time of life

Other hypernyms of second childhood include age, eld, geezerhood, old age.

second childhood (noun)	years (noun)
mental infirmity as a consequence of old age; sometimes shown by foolish infatuations	a late time of life
	a prolonged period of time
	the time during which someone's life continues