The only longitudinal data we have though suggests it doesnt. If my kid was a hell of a center I would have a serious talk as it isn't something I think anyone should do for 20 years. Playing wide reciever in youth football I have no problem.
Do you happen to remember where you saw the longitudinal data? I'm not doubting or disagreeing with you, I am just curious what kind of data they were looking at. For example, did they just look at the population of 75+ year old former players versus non-players, or did they look at the onset of symptoms? I wouldn't be surprised if both populations had similar rates of cognitive decline at old age. But if the former players started showing symptoms at 40 while the general population didn't show symptoms until 70, that would be a major difference. I certainly understand that the "onset of symptoms" data may not have been available since they weren't looking for anything like this 10+ years ago. We can collect this data now, but it might take 20 years to get it compiled and analyzed.
I'll poke around a little over the weekend and see if I can find references to a study like what you described.