Could you provide any research that says that a heavily muscled person is more susceptible to injury due to heavy weights, as his age increases?
The amount of "training knowledge" that is spouted here and on the internet would fill a thimble compared to even a years worth of research in many other fields. It's mostly just pseudoscience and chinese whispers.
You're just parroting shit you've read and a few anecdotal references.
I have no idea if it is an urban myth, but what I do have an idea about is that I don't think you or really anybody knows what the best is for Kevin or if he is actually at risk doing what he does. What do strength guys do when they turn 50? Give in and start hitting the machines? I don't think so.
Fact is, lifting heavy is f u n. It much suck to turn up to the gym to iterate through the myriad machines for 1-2 hours a day 
Cue Basile to come in and warn us all of the dangers of somewhat heavy deadlifting (because it didn't work out for him) and how we should just quit and whittle away our years at the hamstring curl machine
He was having knee and back problems from lifting heavy
He has also torn his pec, lat, and triceps in the past
Doesn't take a genius to figure out lifting heavy all the time is detrimental to the body especially if u are bodybuilding and not powerlifting, it's not rocket science
Guys that have lasted the longest train smart , dexter, jay, Phil, Haney, etc
There are exceptions to heavy lifting for some but almost all end up injured or torn muscles later on due to age and heavy weights, Ronnie, Dorian, Cormier, etc
