This comes up a lot. People are definitely biased towards young, white, males doing most of the coding because it is mostly young white males doing the coding. Part of this is simple demographics. Part of this is confirmation bias. And part of this is our education system and culture filtering out disproportionate amounts of women and non whites who for whatever reason never even get on the career-path for becoming an engineer. Some countries are much worse at this than others.
So the chance of encountering somebody over 40 in a project is about 2^4 or one in 16, assuming lots of people in their early 20s are outnumbering those in their forties. It jumps to 32 for people over 45, 64 for people in their early fifties. I know people who are still coding in their late sixties. I'm 44, and most people I deal with are below 30. Most of the people my age that I know or used to work are by and large still active in the field though a few of them have become managers. Also, seniority means they tend to be big earners and typically too expensive for small projects. Quite a few are doing very lucrative free lance gigs at premium rates, disappeared into big corporations in some senior role, etc.
Uncle Bob has a nice article explaining that the number of programmers doubles every five years: https://blog.cleancoder.com/uncle-bob/2014/06/20/MyLawn.html
So the chance of encountering somebody over 40 in a project is about 2^4 or one in 16, assuming lots of people in their early 20s are outnumbering those in their forties. It jumps to 32 for people over 45, 64 for people in their early fifties. I know people who are still coding in their late sixties. I'm 44, and most people I deal with are below 30. Most of the people my age that I know or used to work are by and large still active in the field though a few of them have become managers. Also, seniority means they tend to be big earners and typically too expensive for small projects. Quite a few are doing very lucrative free lance gigs at premium rates, disappeared into big corporations in some senior role, etc.