Where does “sixties” come from?

Sixties comes from Middle English sixty, the plural or nominal form of the number denoting groups of sixty units.

sixties (English): plural of sixty; API pl; Alternative letter-case...

Definitions

  1. plural of sixty; API pl; Alternative letter-case...

Ancestry of “sixties”, step by step

sixties traces back through two separate lines of ancestry.

via English sixty

StepLanguageWordMeaning
1EnglishsixtyThe cardinal number occurring after fifty-nine...
2Middle Englishsixty
3Old Englishsixtiġsixty
4Proto-Germanicsehs tigiwizsixty

via English Sixties

StepLanguageWordMeaning
1EnglishSixtiesAPI pl; The decade of the 1860s, 1960s, etc; A...
Every word from Proto-Germanic sehs tigiwiz