Longman Dictionary of Contemporary English - sixties

~ n plural 1 the sixties also the '60s the years from 1960 to 1969 2 in your sixties aged from 60 to 69  (early/late sixties)  (I'd say she was in her late sixties.) 3 the numbers from 60 to 69, especially when used to measure temperature  (the low sixties/the upper sixties)  (a fine spring day with the temperature in the upper sixties (=about 68 or 69 degrees))