years vs dotage

years and dotage both are nouns.

Word	Noun	Adjective	Verb	Adverb
years	Yes	No	No	No
dotage	Yes	No	No	No

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

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

Other hyponyms of years include second childhood, senility, autumn years, decrepitude.

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