old age vs age

old age and age both are nouns.

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

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

Other synonyms of old age include eld, geezerhood, years.

old age (noun)	age (noun)
a late time of life	how long something has existed
	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