1. the numbers from 60 to 69, especially when referring to temperature or age
2. the decade from 1960 to 1969

Examples

• The temperature was in the sixties today.
• My grandmother is in her sixties.
• He’s somewhere in his early sixties.
• The sixties were a time of great social change.
• Many famous musicians emerged during the sixties.
• Fashion from the sixties is making a comeback.
• The civil rights movement gained momentum in the sixties.