Wiktionary
undatable
a. 1 Not able to be dated; that may be not be ascribed a date (or age). 2 Not dateable; unsuitable for romantic outings; unattractive.
WordNet
undatable
adj. not capable of being given a date [ant: datable]
Usage examples of "undatable".
In this respect, as the reader will appreciate, the Valley Temple could be compared with a few of the other anonymous and frankly undatable monuments on the Giza plateau, including the great pyramids (and also with a mysterious structure at Abydos known as the Osireion, which we consider in detail in a later chapter) but otherwise bore no resemblance to the typical and well-known products of Ancient Egyptian art and architecture—all copiously decorated, embellished and inscribed.