In early spring I caught the largest fish of my life up in the bay. It was 43 inches long and weighed 23.5 lbs. During the evening a group had a debate on how old it might be. We did some research and there are many factors but found this interesting study done in lakes in Minnesota and in Northern Ontario. The best answer is this fish was between 22-23 years of age.
“With luck, you could live to be 10 years old and reach a length of 36 inches. The average adult Minnesota pike lives about six years, reaches 26 inches in length, and weighs 4 pounds. Rarely, some pike are more than 20 years old and over 50 inches long. The largest pike caught in Minnesota weighed nearly 46 pounds. It was caught in Basswood Lake in Lake County in 1929.”
Here are two links of tables and information about a life of a Northern Pike.
http://www.wildernessisland.com/WalleyePikeAgeSize.php#.VYIBOZXbKM8