age group vs cohort

age group and cohort both are nouns.

Word	Noun	Adjective	Verb	Adverb
age group	Yes	No	No	No
cohort	Yes	No	No	No

As nouns, age group and cohort are synonyms defined as:

age group and cohort: a group of people having approximately the same age

Other synonyms of age group include age bracket.

age group (noun)	cohort (noun)
a group of people having approximately the same age	a band of warriors (originally a unit of a Roman Legion)
	a company of companions or supporters
	a group of people having approximately the same age