sixties vs mid-sixties

sixties and mid-sixties both are nouns.

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

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

sixties (noun)	mid-sixties (noun)
the time of life between 60 and 70	the time of life between 60 and 70
the decade from 1960 to 1969