the.com/sixties

means The ten years from 1960 to 1969, especially as shorthand for the era's cultural upheaval — music, politics, and social change rolled into one decade.

from Just 'six' plus the ordinal-making '-ty' and the plural '-s' — the same pattern that gives us 'twenties' or 'nineties.' Nothing mysterious in the word itself; the mystery is in what the decade did to its own name, turning a plain number into shorthand for revolution, rock music, and upheaval.