I don't think any recent studies on the subject support that claim.
With a few races under my belt this is what I've noticed with the brackets
<20 - Whippersnappers who are on some track team ruining it for the rest of us. Seriously...screw those people.
20-25 - Ex track team members who fill out the top ranks. (The "I'm going to warm up for the 15K race by going for a 5K run")
25-39 - Most of the runners. I was pretty competitive in this group. The occasional top tier person but not to many.
40-50- Something happens where everyone is magically faster (tough bracket)
50-60 - The leathery bastards...how the hell are they keeping pace with everyone? I've seen folks from this group finish to 5 overall.
60-70 - Finishing with the 25-39 crowd
70-80 - Finishing with the "I'm a mom and I'm run\walking to support the slogan of this t-shirt that me and my girlfriends are wearing!!"
80+ - Always seems to be a couple of these folks. Usually honorary mention.
Meanwhile, the dozens of folks I personally know going for knee replacement surgeries are people who don't run or "I love chest day and bicep day" gym rats.