thirties vs mid-thirties

thirties and mid-thirties both are nouns.

Word	Noun	Adjective	Verb	Adverb
thirties	Yes	No	No	No
mid-thirties	Yes	No	No	No

As nouns, thirties and mid-thirties are synonyms defined as:

Other synonyms of thirties include thirty-something.

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