mid-thirties vs thirty-something

mid-thirties and thirty-something both are nouns.

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

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

Other synonyms of mid-thirties include thirties.

mid-thirties (noun)	thirty-something (noun)
the time of life between 30 and 40	the time of life between 30 and 40