senility vs second childhood

senility and second childhood both are nouns.

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

As nouns, senility and second childhood are synonyms defined as:

senility and second childhood: mental infirmity as a consequence of old age; sometimes shown by foolish infatuations

Other synonyms of senility include dotage.

senility (noun)	second childhood (noun)
the state of being senile	mental infirmity as a consequence of old age; sometimes shown by foolish infatuations
mental infirmity as a consequence of old age; sometimes shown by foolish infatuations