dateless

from The American Heritage® Dictionary of the English Language, 5th Edition.

• adjective Having no date whatsoever.
• adjective So ancient that no date can be determined.
• adjective Having no limits in time; timeless.

from The Century Dictionary.

• Having no date; bearing nothing to indicate its date.
• Not distinguishable or divisible by dates; without incident; eventless.
• So old or far distant in time as to be undatable; of indefinitely long duration.

from the GNU version of the Collaborative International Dictionary of English.

• adjective Without date; having no fixed time.
• adjective not having a social companion for an occasion.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• adjective Without a date imprinted, assigned, or associated.
• adjective Having no date—a meeting with a lover or potential lover.
• adjective Timeless; immortal
• adjective Without a start; immemorial
• adjective archaic Without an end; endless
• adjective Out of one's head; deranged.
• adjective UK, dialect, slang thick-headed

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• adjective of such great duration as to preclude the possibility of being assigned a date
• adjective not bearing a date
• adjective unaffected by time
• adjective having no known beginning and presumably no end