I ran numbers from the BLS on occupation data a few years back. If you look at the number of programmers 25-35 in 2000 and the number of programmers in 2020 aged 45-55 you see a real and substantial decrease in absolute terms. The decrease is much larger then other professions, so its not attributable to a cohort just exiting the workforce in general.
There is also a massive increase in the number of 25-35 programmers in the same time period.
My interpretation is there are definitely forces that push against older programmers staying in or re-entering the profession, but they aren’t as severe as they appear to be just looking at the raw numbers. Generally, programmers who want to remain the profession are going to be about to, but it is harder to be a programmer over 40.
Here's [1] a data analysis looking into the phenomenon:
"Professionals with higher cognitive ability drop out of STEM careers earlier and faster", "High-ability workers are faster learners, in all jobs. However, the relative return to ability is higher in careers that change less, because learning gains accumulate"
Some of this is how easy it is to transition from programming to something else compared to other professions. Jumping from building some piece of software to being the expert on it or managing programmers to managing projects etc.
This is especially tempting if someone’s skills start to diverge from what’s in demand.
There is also a massive increase in the number of 25-35 programmers in the same time period.
My interpretation is there are definitely forces that push against older programmers staying in or re-entering the profession, but they aren’t as severe as they appear to be just looking at the raw numbers. Generally, programmers who want to remain the profession are going to be about to, but it is harder to be a programmer over 40.