I'm not sure what you mean by "slopping running" wrt older runners? In the Master's club I've belong to for decades, I've seen guys (and gals) in my age group on up (58+) who don't have the prettiest running form but have been running for decades with that form and very seldom are injured and keep on logging in the miles (and races) year after year. Conversely, I've seen some biomechanically blessed runners in our club who have nothing but constant injuries with some quitting the sport due to frustration.
IMO, I would say it's more about injury propensity & history (some genetics involved there), weight (you're right about that), body type (either thank or blame your parents. Lol) and physiological limitations (bull-legged, pigeon toed, flat fleet, etc - all genetics), and intensity of workouts and races as we get older (over training & racing).
And frankly, aging just like anything else affects older runners differently. And all avid runners who continued to train well into their 60s have to know what they're doing or they wouldn't be there in the first place. They probably know their body better than any sports medicine doctor could analyze. They all have through trial & error found a routine that works for them and I would imagine they know when to back off from over training or altogether shut it down periodically and rest up.
But injuries are huge in this age game. Considering this is a high-impact activity, chronic injuries are probably going to affect most aging runners at one time or another. And acute injuries involving tendon, ligament & muscle tears (and lower back injuries from trauma) can be challenging. Though I was never built for running (short & squatty with flat feet. Lol), I was able to manage ~40 mpw and race year round (mostly 5 & 10s) in my 20s, 30s & 40s with minimal injuries. But I was addicted to speedwork & hard racing for the endorphin rush. Never backing off in my 50s, the big time ruptures & strains (Achilles, patellar tendon, posterior tIbial tendon, hamstrings ) started to occur over a span of several years. And trying to run through some of the injuries didn't help matters either and caused re-tears in some cases (those damn endorphins!). Also, add a MV accident where a knucklehead texting blew a red light broadsiding me (while driving home from race nonetheless!) causing a significant back and upper body injuries. And torn tendons, ligaments, muscles, etc. don't act or respond the same as uninjured tissue and invariably can lead to OA if a joint is involved. So, if aging runners can avoid acute tears & strains, any chronic injuries can be more easily managed with the right rehab & modification.
Walking is great and I've have to add more walking in place of run days lately (which is only 3 days a week anyway). And 4 days a week at the gym for spin bike cross training, strength training & rehab excercises (I'm in a constant state of rehab. ?) gets monotonous afterwhile. The only thing I don't like about walking is the slower pace and lower heartrate (and lower perceived rate of exertion) where I don't get those endorphins and end up feeling unfulfilled. So, I'm experimenting with some speed walking/race walking and see if it elevates the HR and more towards maybe 75 or 80% of my VO2max
Anyone here incorporate RW as part of your training?
Interestingly, this study showed RW demonstrated 46% lower impact forces in comparison to running:
https://www.researchgate.net/publication/313625727_Is_Race_Walking_Lower_Impact_Than_Running