years vs old age

years and old age both are nouns.

Word	Noun	Adjective	Verb	Adverb
years	Yes	No	No	No
old age	Yes	No	No	No

As nouns, years and old age are synonyms defined as:

Other synonyms of years include age, eld, geezerhood.

years (noun)	old age (noun)
a late time of life	a late time of life
a prolonged period of time
the time during which someone's life continues