That does not mean the will to live is not real, and those without out it fade much faster.
My dad lead a VERY active lifestyle - triathlons, squash, swimming, working on building sites, etc. What reward did he get for all that exercise and activity? Replacement hips, painful knees and developing spinal issues (spinal stenosis I think, but can’t quite remember off the top of my head) that he’s been told to live with until he can’t stand the pain anymore because surgery is incredibly risky and might not help or make things worse.
He does have great cardiovascular health though and he still works at his own business, learned how to use an iPhone, etc. Still walks a ridiculous number of steps a day that puts me to shame. The mechanical issues do make it more difficult than it used to be for him though.
It motivated him to completely alter his diet when the doctor said so, take up physical therapy when the doctor said so, and all manner of other healthy life choices that most people just wouldn’t bother with so late in life.
Good reason to live is a massive part of making choices that keep you living.
My great grandmother just died at 90 and really what killed her was being forced to stop walking, she lost so much bone mass that the increased Gs in elevator buckled her shin.
The other had one of his lungs shot by tuberculosis, but despite that, smoked his entire life. Not particularly active either after retirement. He lived until his late 80s (EDIT: just checked, 85 actually).
EDIT: Obviously staying active is important for good health but anecdotes are not super informative.
Or, so I tell myself, as almost all of the men in my family have lived to be over 100 years old, so I have hope that I may do the same.
Alas, that's not the lifestyle for me.
I've noticed this kind of thing as well, but I'm really worried that we have cause and effect backwards.
The one who sat and did nothing did that because of poor health, rather than poor health because he sat.
Truthfully I believe it's strength training that actually helps keep them up. Could be wrong.
A mobile lifestyle is good, obesity is bad.
Probably this thinking comes from "ghost in the shell" mixed with Asimov's books.
Likewise, maybe the latter had great cellular health and it enabled him to be more active without feeling awful.
You just stated that he’s genetically predisposed, but you believe lifestyle choices are the main driver here?
Both my Grandfathers retired shortly before seventy. One sat down in his Chair and did not get up. He ignored his health, and passed within 10 years.
The other is highly active in his community and church, still gardens, and travels constantly. He is in his mid 80s with no sign of slowing down. Barring a major health incident, he will live well into his 90s like his mother, and may pass 100.
Not doing anything is bad for your health, both physical and mental. The effects are exacerbated when you are older, but are still prevalent when younger.