I certainly subscribe to the theory that your body slows in recovery time with age, and also cannot tolerate certain kinds of abuses that it was able to tolerate when younger... and some of those behaviors that we did as a younger person might end up killing us as an older person, so in that sense, I would take with a grain of salt about the idea that "whatever doesn't kill you, will make you stronger".. since that is likely a younger man's phenomena..

...even though it is probably that our bodies do likely need some stressors to become stronger even though at some point we are not as able to even tolerate various stressors, so we have to make the stressors weaker in order to become stronger and we might not even be able to get up to close to the levels of our previous tolerances.. and even now there are some things that I just am not able to do, and I am not prepared to train 24/7 in order to try to get up to being able to do certain things that I could do in my 20s, and my training might not end up getting me to those levels anyhow, so then I just ended up wasting my time on goals that I am not able to achieve while neglecting some other areas of my life that are also important.