I also know very in shape and healthy elderly people, and it really doesn't matter in the end. They're still slower, weaker, in pain, and things aren't working optimally. They still recover way slower than when they were young. They're still at risk of a minor fall or illness causing them to wind up bedridden.
Staying in shape and trying to be as healthy as you can be at any age is a good thing. I'm not saying you shouldn't do that. But in the end, it doesn't matter how well you take care of yourself, once you reach a certain age, minor injuries or illnesses can take you out. A lot of the people I worked with in nursing homes were not people that were unhealthy slobs, there were plenty that worked out and ate right their entire lives. Aging sucks and even the people who don't mind getting older will tell you that if there was a magical pill that would make them young again, they would take it in a heart beat.
That's the thing. The definition of "old person" has changed dramatically. The fact that on average we are loving till 75 going on 80 is in itself a world changing epiphany. No one in their 20s-30s should be struggling with "old people diseases" we have the know how and the tech to reverse them easily but to say that having a majority of the population struggle with this en masse is unheard of is comically wrong. It's not an "achtually I know a 6'3 Thai guy" thing even if you weren't rich enough to have gout these ailments have haunted the younger ends of adulthood for as long as stress and malnutrition have,which is to say a really damn long time. The REAL concerning thing is despite living in the ACTUAL FUTURE with conversation having robots and little dingy motorized foot scooter thingeys we STILL haven't engrained in the popular zeitgeist that eating meat won't give you a heart attack and eating only bread isn't going to save you either. We live on the golden age of easily accessible information and yet so many people still act like they are completely HELPLESS. No wonder people like Bryan Johnson are allowed to persist. People still think healthy diet and exercise are a thing only richy rich richerson people have and have yet to realize they can grow their own crap for cheap just by following a YouTube video or something.
Staying in peak physical health is a noble goal, but even people I know who lead extremely healthy or unhealthy lifestyles and are now in the later stages of their lives, no matter how active they are, have mental problems - stuff like Alzheimer's, dementia and many others.
I'm not sure what Bryan Johnson has said about that stuff and there are some neuroprotective medications as well as ones that increase neuroplasticity (basically making new brain cells, which is what ketamine does) and also some lifestyle factors that can impact it but whether or not that stuff works when people are 80 can make a difference is totally unknown AFAIK.
Some issues like Alzheimer's are heavily related to genetics - I have a relative who has early onset dementia and is totally mentally gone which is a very painful and distressing thing to see. One of their children told me that the relative had earlier said "if I ever end up like that, take me out the back and shoot me". Watching someone who was previously full of life degrade to where they keep repeating questions and then degrade even further to the point they can't even recognize anyone and can get very agitated is a very sad thing to see.
Thankfully my genetics aren't quite as bad as theirs were when it comes to Alzheimer's but I still have a
significantly large number of genes relating to Alzheimer's and there's a very real and distinct possibility that I even get it early onset and it raises big questions about longevity and planning for end of life. I kind of wish I never got my genetics tested for that reason because it is a shadow that doesn't quite go away and does impact how you look at life very much because there's an omnipresent clock ticking throughout the day.
All this is to say while you can do a whole bunch of tests relating to your physical health and shit like erections during the night its very clear there is a significant role in genetics when it comes to the brain in older age. There are some people in their 90s who are sharp as a tack and have been smoking cigarettes and drinking liquor every day of their life and some people who do everything right and get hit with sudden terminal cancer very suddenly or end up with issues in their brain that are seemingly predetermined by their genetics or perhaps environmental factor.
Anyway, all I'll say is if you don't have a will already make one and if you have knowledge that you might be very likely to get impacted by certain conditions then you can make provisions for if that actually happens. I know most people aren't a fan of assisted suicide etc but I can fully understand why its a necessary thing for people near the end of their lives.
Failing that (or in addition to that) you can also make a will that enables you to get cryogenically frozen but its not cheap and you have to be "frozen" ASAP after you pass away:
https://web.archive.org/web/20140829123055/https://www.wired.com/2014/08/hal-finney/ and if you're lucky they'll figure out a way to defrost you later on and also by that time figure out a way to fix the illness you had when you died.
