What exactly is your thesis? What do you maintain the age of opponents indicates? You have Dempsey on this post, so let's take two of his opponents. Carpentier was 27 when he fought Dempsey. Gibbons was 32. Experience? But Carpentier had been fighting 14 years to Gibbons 12. Ability? But Gibbons defeated Carpentier in 1924 when he was 33 and Carpentier 30. So what exactly does an age comparison between these two opponents prove about Dempsey's competition? I understand your point about filtering out the tomato cans. I don't understand what you are saying about age and the quality of opposition.
There is no "thesis". It is just the average age of the non-bums on each major heavyweight champs resume starting from Dempsey onward. Take from it what you will. How would the age of Gibbons and Carpentier when they fought have anything to do with Dempsey?