The closer I get to my forties, the more important it is to take care of my body. Basically, you just realize that your body is not what it used to be, and you have either the choice to do something to stay/get back in shape (more sports, a better diet), or let it go (which is, unfortunately, the first step to health complications).
There is also a strong bias regarding to whom you hang with then. Being "seriously" involved in any sport means that you are going to dedicate a significant part of your free time to training, and therefore, will spent much more time with your fellow sportsmates than "regular" friends.
I always wonder how the people over 40 training for a triathlon do in the long run. Do they accumulate more and more problems until they can't do it anymore? How do they handle injuries that don't allow them to run anymore?
https://en.wikipedia.org/wiki/Madonna_Buder#Triathlon_career
Used to teach yoga classes. During seminars you could see older famous teachers do amazing stuff. I thought yoga is is really healthy until I found out that a lot of them had hip and knee replacements and often lived in painkillers.
I believe most people simply can't do high intensity stuff from a certain age on or have to be very selective.
It's bi-modal isn't it?
Half of people are fatter than ever, the other half are fitnesses obsessed. There's not as much moderation in the middle as there sued to be.
Now, they've similarly "defaulted" into the lifestyle and eating habits that are available to them, but those are worse for their health.