I think a lot of the "I don't see >40y/o swe" is a combo of:
There were more CS/IT grads from 2000 to today (<40 years old) than were ever produced prior to year 2000.
After 40 you tend to move into management, consulting, or just switch careers, b/c SWE pays well.
After 40 you don't work at companies that churn through young devs (so young devs are less likely to work with > 40 y/o)
I think a lot of the "I don't see >40y/o swe" is a combo of:
There were more CS/IT grads from 2000 to today (<40 years old) than were ever produced prior to year 2000.
After 40 you tend to move into management, consulting, or just switch careers, b/c SWE pays well.
After 40 you don't work at companies that churn through young devs (so young devs are less likely to work with > 40 y/o)