That’s specific to my area but I wouldn’t doubt it’s nearly universal. Old animals/fish of any species hit a point of diminishing returns. A 5 lb smallmouth is basically a grandma, not exactly in peak reproductive shape. They still nest but the number of healthy eggs starts to diminish. Peak breeding occurs in the “prime” years
this is why almost any fish has a length minimum for keeping. Once they are over a certain length, they have successfully bred a few seasons. If the oldest fish were the best breeders, the biologists would let you keep small fish and not big ones