Source : Webster's Revised Unabridged Dictionary (1913)

Sexagenarian \Sex`a*ge*na"ri*an\, n. [See {Sexagenary}.]
   A person who is sixty years old.

Source : WordNet®

sexagenarian
     adj : being from 60 to 69 years old; "the sexagenarian population
           is growing"
     n : someone whose age is in the sixties