old是老的，hill是小山，as old as the hills字面意识像山丘一样古老，也就是古老的；悠久的。

【例句】
As vales are as old as the hills, so loughs and rivers must be as old as they.
随着时间的发展，人们通常用这个习语来形容某事物非常古老。

Many of the tribe's customs and rituals are as old as the hills.
这部落的许多风俗、仪式都极其古老。