senility vs eld

senility and eld both are nouns.

Word	Noun	Adjective	Verb	Adverb
senility	Yes	No	No	No
eld	Yes	No	No	No

As nouns, eld is a hypernym of senility; that is, eld is a word with a broader meaning than senility:

senility: mental infirmity as a consequence of old age; sometimes shown by foolish infatuations
eld: a late time of life

Other hypernyms of senility include age, geezerhood, old age, years.

senility (noun)	eld (noun)
the state of being senile	a late time of life
mental infirmity as a consequence of old age; sometimes shown by foolish infatuations	a time of life (usually defined in years) at which some particular qualification or power arises