I would say people with good genetics can push it to the limits, i.e., train hard year round with minimal risk of injury. I see it all time in the masters running club I belong to with the genetically gifted athletes. Generally speaking, these are lighter weight, smaller framed runners with great biomechanics. For some of us though, not so fortunate.
I'm in my mid-50s, with a significant injury history that's regulated me to more of a fitness runner (or as those "arrogant" elite runners like to characterize us as the proverbial "hobby joggers" 😕). I was never built like a traditional distance runner being a football player & sprinter in high school. Now at 160 lbs (5-7), I'm at my high-school weight and about as lean as I can get without resorting to pharmaceuticals, or literally starving myself (runners that can maintain a good matabolism as they age without straving themselves are very lucky).
When I was in my late 40s, I was fairly injury-free and though not as fast as most here on this forum (my goodness...is an "elite" 50+ master's forum with some of the times these folks run?), I could consistently hit sub-20 5ks and run 5: 25 or so in a track mile (at 165 lbs). Now over the last couple of years, I've had an Achilles strain, a patellar tendon strain, hamstring strains, a complete ruptured PTT of the ankle and a major heat exhaustion incident ..all causing many months of missed running and a lot of pain. So, thank goodness for indoor spin bikes...I can get some decent workouts without feeling all beat-up (though the spin bike is nothing like running). And in addition to the cross training, I have a daily life of icing, stretching, rehab...all to run a precious 15 or so mpw and maybe a couple of 5ks a year.
So, if you're generally light & small in statue, and are genetically gifted with great biomechanics (i.e., like the Kenyans are)...then you have the edge and can put in the miles and hard training necessary to run fast and injury-free well into your old age (studies have shown that runners with good biomechanics have far less chronic injuries than those who don't...even at the elite level). And for those of us not so genetically gifted and develop chronic injuries, all we can do is live & rehab to run another day 😑.