dateless

1. Having no date whatsoever.
2. So ancient that no date can be determined.
3. Having no limits in time; timeless.

adjective

Existing unchanged forever: ageless, eternal, timeless. Archaic eterne. See change/persist.

The adjective has 4 meanings:

Meaning #1: having no known beginning and presumably no end
  Synonyms: endless, sempiternal

Meaning #2: of such great duration as to preclude the possibility of being assigned a date

Meaning #3: not bearing a date
  Synonym: undated

Meaning #4: unaffected by time
  Synonym: timeless