The phrase "age old idea" is correct and usable in written English.
It can be used to refer to a concept or belief that has been around for a very long time and is often considered traditional or timeless.
Example: "The notion of love conquering all is an age old idea that has been explored in literature for centuries."
Alternatives: "ancient concept" or "time-honored belief".
"She's suddenly become a symbol of the status quo — old times, old age, old ideas," said Hahm Sung-deuk, a political scientist at Korea University.
The one-child policy has helped erase the age-old idea that girls are not as valuable as boys.
The solution, she says, lies in an age-old idea: buy high-quality pieces and less frequently.
"Well, they're due a big one in Wellington," one resident tells me, voicing the age-old idea that everything bad starts in the capital.
Over the past decade, it has become a rebuke to the age-old idea that London food, and British habits of eating, are a lousy joke.
It really all goes back to the age-old idea of trying to be all things to all people — once a brand starts to do this, it falls into a trap that experts warn about.
More than this, by offering the egg freezing funding, these businesses reinforce the age-old idea that reproductive decision-making – and family planning – is the responsibility of women alone.
The first is that this age-old idea of "clearing the field" for a preferred candidate, so as to avoid divisive primaries, is now, much like the old party clubhouse, a historical relic.
It consists of a square carved out from the white gallery wall to reveal the wall's essence, in effect creating the wall's self-portrait while also rebuffing the age-old idea that art hung on it is a view to another world.
But many commentators felt the patronising off-the-cuff "Calm down dear" revealed Cameron's true nature; years of careful modernising of the Tory image undone with a single remark that instantly conjured up the age-old idea that women were hysterical creatures incapable of rational thought.
