NOUN (1)

1. someone whose age is in the sixties;


ADJECTIVE (1)

1. being from 60 to 69 years old;
- Example: "the sexagenarian population is growing"

The Collaborative International Dictionary of English v.0.48:

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

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

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