Hippie era, with 'The'

• "Peace" time?
• "Flower Power" era
• Late decade
• Decade with tie-dyed shirts and miniskirts
• Decade when ZIP codes were introduced
• The time of life between 60 and 70
• Number of fashion items in Mary Quant's era

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1848 as the years of someone's life between 60 and 69; 1827 as the seventh decade of years in a given century. See sixty .

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Sixty \Six"ty\, n.; pl. Sixties . The sum of six times ten; sixty units or objects. A symbol representing sixty units, as 60, lx., or LX.