I decided a while ago that I'm going to live my life as if this were true despite not having scientific evidence to support it. When people retire they're in danger of rapid decline if they stop living a rich and active life, exactly as you said. You need physical, mental, and social stimulation. My grandmother is in her 90s and doing really well considering her age, and I can see that she walks, read books, and meets friends all the time. I pursue physical and mental stimulation constantly; running, yoga, lifting weights, practice music, learn new languages, programming, reading books, etc. (I admit I have a bad habit of neglecting social needs.) If I am lucky enough to "retire young" from software I plan on pursuing a new career in some passion field. I've chosen to believe that slowing down is my choice and right now I plan to choose not to.

I know all of this is anecdotal, you can go ahead and preface every sentence I wrote with "I think/In my opinion..." but in this case n really does equal 1, I only have 1 life to live. Even if there is absolutely no correlation between my observations and reality, with this strategy I'm only at risk of a life well lived.