40 is an interesting age to choose for this. I don't know if this still holds true, but back in the day it seemed like a pro wrestler didn't really hit his peak prime (I guess meaning a combination of physical abilities plus mentally getting the business, psychology, etc.) until his early-to-mid 30s. But maybe that's partly a result of many guys getting into pro wrestling back in the day as a second career or fallback?
On first pass, initial thoughts were maybe we as fans and he as a wrestler would have be better off if Bret did retire in 1997.