The phrase "an old myth" is correct and usable in written English.
It can be used when referring to a traditional story or belief that is widely held but not necessarily based on fact.
Example: "The idea that humans only use 10% of their brains is an old myth that has been debunked by scientists."
Alternatives: "a long-standing myth" or "a traditional myth".
"That's an old myth," Ms. Ginsberg said.
Whatever else Sunday's turnout shows, Mr. DeGolyer said, it may demolish an old myth.
It's an old myth that we can't and shouldn't be friends with people at work.
By Daniel Mendelsohn Colm Tóibín's "House of Names" seeks to give an old myth a new set of meanings.
Kirsty Hughes Chief executive, Index on Censorship It's sad to see an old myth still being perpetuated (Report, 16 May).
Airbrushed, stylised representations of a new version of an old myth, not much to do with the dead carnation heads on their graves.
That toy is dangerous!"' Some would call this paranoia, but years of viewer response have proved to the Koziks that paranoia, like privacy, is a rather quaint concept -- a dear old myth of yesteryear.
There's a pernicious old myth that claims the word handicap refers to beggars, wounded by war and so unable to work, relying on begging with their upturned caps in their hands just to make ends meet.
The story of Saint George and the dragon has long seemed like a barmy old myth, way out of kilter with the nation that our patron saint is meant to represent.
Once again this is a tired old myth that rears its head constantly despite the fact it's silly and empty of truth.
"By basing his story on one of the most popular books of the Middle Ages and Renaissance, Adams taps into a very old myth: the flight from disaster, the heroic refugee in search of a new home, a story that was already over a thousand years old when Virgil told it in 19 BC".
