The old guy has prostate cancer. Apparently, this was brewing for years, without giving the slightest sign. All the tests have a high 'false negative' rate. pc is a very weird thing. It can be so slow that it will never be a problem. So, all the people that are diagnosed in their 60's get treatment with radioactive beads and such, and none of that might be worth it.
The old guy has Super Sneaky Prostate Cancer, but he's 86. It knocked him down earlier with urinary problems and they treated it as a benign prostate enlargement. Finally, it hit his legs, and only a full bone scan showed it.
When it gets into the bones, it causes massive calcium problems. This gets the muscles very upset, and they probably pour out calcium, lose mass and go weak. The good news is that they have started hormone therapy, which starves the little buggers, and he can recover.
Now he is looking at several years, which is as good as any of us get. I'll be working hard on his brain, which is unaffected.
Speaking of the brain, I just got this little Chromebook, which is almost bullet-proof and waterproof. I love using it, and he'll get it. Also, a big Pixel 2 xl, which is set up for large print, and total vocal command. This arrangement is fantastic for old guys and we'll be doing philosophical arguments over the internet. I'm all for hard physics, and he's getting ensteinily mystical. :)