How do we know all of these anecdotes (on Quora and here) aren't survivorship bias? How many people have left software development in their 40's, for something

How do we know all of these anecdotes (on Quora and here) aren't survivorship bias? How many people have left software development in their 40's, for something else (management, etc)? Specifically, can we get figures to back it up, and not just lists of anecdotes? Because in my own anecdotal experience I have always have had more peers younger than me than older than me, across my ~15 years of engineering (I'm in my early 40's, and started programming as a career late).