old as the hills

To be old as the hills means to be exceedingly old, and may be used in reference to people or things, but is most commonly used for people. Saying someone or something is old as the hills is a way to exaggerate how old someone or something really is. You will hear this phrase spoken about a person who is old, whether sarcastic or not, as a way to describe their advanced age; occasionally it is used in reference to a thing.