oldness vs senility

oldness and senility both are nouns.

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

As nouns, senility is a hyponym of oldness; that is, senility is a word with a more specific, narrower meaning than oldness:

Other hyponyms of oldness include agedness, senescence, longevity, seniority, staleness.

oldness (noun)	senility (noun)
the quality of being old; the opposite of newness	the state of being senile
the opposite of youngness	mental infirmity as a consequence of old age; sometimes shown by foolish infatuations