I'm lucky: I switched into a role where deep domain experience is essential, I did a PhD, I'm one of the top experts in a growing field - I'm more or less insulated from this. Indeed, now I hire people and I'm actually one of the perpetrators of it. We get resumes, I look at them, and inevitably many of the younger people are both (a) cheaper and (b) more on-target with their skill sets. Then there is a much more subtle and non-explicit discrimination on top of that which involves a presumption that an experienced person will not be "happy" working in what they would perceive as a junior level role. That they would find another position and leave. So they honestly can't win - if they don't have the skills they don't get hired, if they do, it is presumed they are too experienced to be happy in the job.
There must be a massive wave of ageing developers that is coming that is 10x the size of what we have seen so far. Something will have to change somewhere, hopefully it will help us all discard some of these discriminatory practices.