So how did it get to be 512-years-old? According to The Washington Post, it is mostly because of the margin for error attached to the scientist's study. While they estimate that 272 is the correct age, there is a margin that states the shark could also be older:
The scientists had to use creative methods to estimate the ages of 28 Greenland sharks they'd captured.
They used radiocarbon dating to determine that most of the specimens predated nuclear bomb tests, which began in the 1950s. Then they extrapolated from the shark's extremely slow growth rate that the largest was likely just shy of four centuries old.
But given the margins of error, the shark could have been as young as 272 or as old as 512 — thus, the Daily Star's screaming headline about “Ancient LIVING shark born in 1500s.”
So it starts with one tabloid, then another, and soon we have a shark that is older than Shakespeare swimming around. It also shows that some news can truly stand the test of the time, since the study was from 2016 and people are still writing about it.