I understand the motivation behind this advice, but now that I'm past 50, I'd say that everyone needs to decide for themselves whether they are still pushing to maintain youth, or whether they are deliberately embracing aging.
At some point, you stop exercising "hard", and start exercising "enough". The point is the same - to stay healthy. But you are not going to hit your lifetime peak fitness. Instead, you want to build a solid base of strength so that you still are fully capable and mobile into your 70s and 80s.
As far as staying up on tech, again that depends on how long you really want to be in tech. Some people may want to remain technical for a couple more decades... but some of us are happy to let others take the lead, while we settle back into secondary positions, or pivot our ambition to leadership instead of hands-on work.
What I'd recommend is some deep introspection to decide for yourself whether you are young or old, and act accordingly. "old" !== "bad". It is more a decision of whether you are still climbing, or simply enjoying the ride at a comfortable cruising altitude. I might not get hired by startups or FAANG for being in cruising mode, but once you get to this point, you aren't interested in such jobs anyway.
The point is to figure out what is right for yourself, and don't push youth too far. There are natural changes to the pace of life as you age, and acceptance of that helps life satisfaction.