age vs autumn years

age and autumn years both are nouns.

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

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

age: a late time of life
autumn years: (literary) the later years of one's life, especially after one has finished their career.

Other hyponyms of age include dotage, second childhood, senility, decrepitude.

age (noun)	autumn years (noun)
how long something has existed	(literary) the later years of one's life, especially after one has finished their career.
a time of life (usually defined in years) at which some particular qualification or power arises
a late time of life
an era of history having some distinctive feature
a prolonged period of time