The Collaborative International Dictionary of English v.0.48:

Ageless \Age"less\ ([=a]j"l[e^]s), a.
   Without old age limits of duration; as, fountains of ageless
   youth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ageless
    adj 1: continuing forever or indefinitely; "the ageless themes
           of love and revenge"; "eternal truths"; "life
           everlasting"; "hell's perpetual fires"; "the unending
           bliss of heaven" [syn: ageless, aeonian, eonian,
           eternal, everlasting, perpetual, unending,
           unceasing]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "ageless":
   age-old, ancient, antique, auld, ceaseless, coeternal, constant,
   continual, continuous, dateless, elderly, endless, eternal, eterne,
   ever-being, ever-durable, ever-during, everlasting, everliving,
   hoary, immemorial, incessant, indestructible, infinite,
   interminable, never-ceasing, never-ending, nonstop, nonterminating,
   nonterminous, of old, of yore, olamic, old, old as Methuselah,
   old as history, old as time, old-time, olden, perdurable,
   permanent, perpetual, sempiternal, steady, timeless, unceasing,
   unending, unintermitting, uninterrupted, unremitting, venerable,
   without end