sexagenarian

sexagenarian
    adj 1: being from 60 to 69 years old; "the sexagenarian
           population is growing"
    n 1: someone whose age is in the sixties
    

Sexagenarian \Sex`a*ge*na"ri*an\, n. [See {Sexagenary}.]
   A person who is sixty years old.
   [1913 Webster]
    

84 Moby Thesaurus words for "sexagenarian":
      Father Time, L, Methuselah, Nestor, Old Paar, Sexagesima, boxcar,
      boxcars, centenarian, dotard, dozen, duodecimo, eighty, elder,
      eleven, fifteen, fifty, five and twenty, fortnight, forty,
      four and twenty, fourscore, fourscore and ten, fourteen, gaffer,
      geezer, golden-ager, gramps, grandfather, grandsire, graybeard,
      half a hundred, long dozen, ninety, nonagenarian, octogenarian,
      old chap, old codger, old dog, old duffer, old geezer, old gent,
      old gentleman, old man, old party, old-timer, older, oldster,
      pantaloon, patriarch, presbyter, quindecennial, quindecim,
      quindecima, quindene, score, senior citizen, septuagenarian,
      seventy, sexagenary, sexagesimo-quarto, sixteen, sixteenmo, sixty,
      sixty-four, sixty-fourmo, teens, the quiet-voiced elders, thirteen,
      thirty-two, thirty-twomo, threescore, threescore and ten, twelve,
      twelvemo, twenty, twenty-five, twenty-four, twenty-fourmo,
      two dozen, two weeks, twoscore, venerable sir, veteran