The phrase 'Be as Old as the Hills' means that if something is as old as the hills, it has existed for a very long time.
Example of Use: "Difficult relationships between parents and children are nothing new: the problem's as old as the hills."
The origin of the idiom 'as old as the hills' is biblical. The phrase is derived from Job, 15:7 and was first seen in the 1535 Miles Coverdale’s Bible: “Art thou the first man, that euer was borne? Or wast thou made before the hylles?” The idiom did not gain popularity in its current form until 1734, when Francis Hutchinson’s A Defense of the Ancient Historians read: “As vales are old as the hills, so loughs and rivers must be as old as they.”