second childhood vs age

second childhood and age both are nouns.

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

As nouns, age is a hypernym of second childhood; that is, age 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
age: a late time of life

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

second childhood (noun)	age (noun)
mental infirmity as a consequence of old age; sometimes shown by foolish infatuations	how long something has existed
	a time of life (usually defined in years) at which some particular qualification or power arises
	a late time of life
	an era of history having some distinctive feature
	a prolonged period of time