I didn't quite make it to forty years, but I think I could say I made it to 37 (1983-2020). I've also spent more time than the average programmer writing on a computer, and I've never had any significant RSI-type issues. This might be a bit controversial, but I think part of the reason is that I'm not a traditional touch typist. That's not to say I'm slow, either. I've probably worked with well over a thousand other programmers, and the only person I'm sure was faster wasn't any of them. It was my mother, who was a professional typesetter longer than I was a professional programmer. Only a handful of other programmers have even seemed close.
So, why do I think that relates to my lack of RSI problems? Because with my seven(ish) finger method my hands constantly rove over the keyboard. What they don't do is stay in one fixed location, with the wrists in the same (usually somewhat awkward) position as only the fingers move. That maximizes repetition - the R in RSI. Minimizing hand motion this way is bad. If you want your hands and wrists to stay healthy you have to keep them moving, just like any other muscle/tendon/ligament complex in any other part of your body. It's silly to think that the general rules of exercise and flexibility don't apply to hands.
So, why do I think that relates to my lack of RSI problems? Because with my seven(ish) finger method my hands constantly rove over the keyboard. What they don't do is stay in one fixed location, with the wrists in the same (usually somewhat awkward) position as only the fingers move. That maximizes repetition - the R in RSI. Minimizing hand motion this way is bad. If you want your hands and wrists to stay healthy you have to keep them moving, just like any other muscle/tendon/ligament complex in any other part of your body. It's silly to think that the general rules of exercise and flexibility don't apply to hands.