The 5.3-metre long shark was listed last summer on the Discovery Channel as No.2 on its list of top five legendary sharks.
Now researchers have found the shark was still a youngster with a lot of growing to do.
New studies in the U.S. and Canada that examined the P.E.I. shark's bones, along with others, show that sharks grow more slowly and mature much later than previously thought. The research gives precise dating of the age of sharks by looking for evidence of exposure to radioactive fallout from nuclear weapons testing in the 1950s and 60s.
The researchers determined great whites live for about 70 years, and don't mature until age 30. The P.E.I. shark was just 20 years old.
"It's a teenager in shark years," said Steven Campana, head of the Canadian Shark Research Lab at the Bedford Institute of Oceanography in Nova Scotia.
"If it would have lived longer it would have gotten a lot bigger. It was a female at 5.3 metres long. It was a big shark, but it still had a lot of growing to do."
Last year, Canada listed great white sharks as an endangered species. Campana said the new research is important, because discovering the late age of maturity means scientists now understand shark populations will recover much more slowly than previously thought.