Having no known beginning and presumably no end:
— The dateless rise and fall of the tides.

synoniemen: endless, sempiternal.

Of such great duration as to preclude the possibility of being assigned a date.

Not bearing a date:
— A dateless letter.

synoniem: undated.

Unaffected by time:
— Few characters are so dateless as Hamlet.

synoniem: timeless.

Pools: ponadczasowy, bezczasowy