When I was a warden at Grafenwohr, Germany. We had one in one of the Lakes that was the same length as a canoe. We estimated it to weigh in the 500 lb range. Was thinking about using a cat for bait (just kidding). In the danube they get over 600 lbs.
They can live for well over 100 years. They can attain 5lbs by the third year, 180 lb by 24 years and take another 60 years to reach 500 lb. So the 19th century Russian specimens of 15 ft and 750 lb would be substantially older.
The lake was on the north end of the impact area and the only time you where allowed to fish it, was when they had the yearly Northern Pike tournament, which was only one day event. We had a chance to go back there when the range was shutdown, did not fish just scouting.
They do get some monster Northerns over there…Anyone see that show where the dude was fishing with the drunk Russian guide on the Caspian sea for Sturgeon where they were catching huge northerns early in the day? AWESOME! You could see shots of the guide taking swigs from his vodka bottle.