How old is Hanging Gardens of Babylon?

Answer 1

According to Wikipedia: The gardens were attributed to the Neo-Babylonian king Nebuchadnezzar II, who ruled between 605 and 562 BC. He is reported to have constructed the gardens to please his homesick wife, Amytis of Media, who longed for the plants of her homeland. The gardens were said to have been destroyed by several earthquakes after the 2nd century BC.

That would make them roughly 2500 years old, and they would have been destroyed around 2200 years ago. It should be noted, however, that there is some dispute as to whether they ever actually existed.

Also from Wikipedia: A recent theory proposes that the Hanging Gardens of Babylon were actually constructed by the Assyrian king Sennacherib (reigned 705 - 681 BC) for his palace at Nineveh. Stephanie Dalley posits that during the intervening centuries the two sites became confused, and the extensive gardens at Sennacherib's palace were attributed to Nebuchadnezzar II's Babylon.