thirties vs thirty-something

thirties and thirty-something both are nouns.

Word	Noun	Adjective	Verb	Adverb
thirties	Yes	No	No	No
thirty-something	Yes	No	No	No

As nouns, thirties and thirty-something are synonyms defined as:

Other synonyms of thirties include mid-thirties.

thirties (noun)	thirty-something (noun)
the time of life between 30 and 40	the time of life between 30 and 40
the decade from 1930 to 1939