cohort vs age group

cohort and age group both are nouns.

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

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

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

Other synonyms of cohort include age bracket.

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