The Grand Canyon, geologically speaking, wasn't always one thing. So, although we think of it as a single, incredible phenonmenon, the canyon is, simultaneously, very old and very new. New research has shown that the canyon as a whole is just a few million years old, but some sections are much, much older. In other words, the Grand Canyon is a patchwork, a series of canyons that only recently came to be a single grand canyon.
As the mighty Colorado River courses through the intermountain west down to Mexico, rushing water carves away at rock. Some researchers have argued that the Colorado River created the Grand Canyon, by carving the deep trench as recently as 5 to 6 million years ago. Other scientists, however, thought the Canyon was much older, as much as 55 to 70 million years old. This line of thinking had it that older rivers carved the deep chasm, with more modern flows having relatively little effect.
The team found that two stretches near the canyon's middle are indeed quite ancient: the eastern Grand Canyon is 15‒25 million years old, and another stretch downriver is 50‒70 million years old.
But the researchers also found that two other segments — Marble Canyon, the farthest stretch upriver studied, plus the westernmost Grand Canyon — were carved far more recently. “Different segments of the canyon have different histories and different ages, but they didn’t get linked together to form the Grand Canyon with the Colorado River running through it until 5 to 6 million years ago,” says Karlstrom.
The BBC: ""If you were to add up the 280-mile length and ask, 'how much is young? More than half of it is young; a quarter of it is middle-aged - 15-25 million years old; and the rest of it is 70 million years old," said Prof Karlstrom."
The true age of the Grand Canyon then, is a matter of definition. The Grand Canyon as a whole, well, it is young—but you could say it has an old soul.