The creosote bush in the Southwest US has been dated at just under 12, 000 years old because of its cloning abilities. Is each specimen that old? Not if you count the rings.
For what its worth: I work as a naturalist in a giant sequoia grove. At one point years ago, we used to claim that the Sequoiadendron giagantium was the world's largest living thing. Since then we have been told to modify that statement since groves of aspen trees are rhizome clones, each tree sprouting from a single root source. So I guess the National Park Service would call this oak a singular tree.
Of course it really doesn't matter which tree is the oldest, the tallest, or the largest. They're all pretty cool!