[lordCarbonFiber]

I think a lot of what gets seen as ageism is push back against the explosion of "software developers" (i use this term very loosly) that cropped up during the dot com boom. Especially in industries that aren't purely tech (finance, healthcare) a lot of really terrible developers have found lasting success just riding on percieved experience. After enough time interviewing these sorts of folks it takes effort not to form biases or let them precolor your experience with new candidates. Believing the that experience implies wisdom can be a trap. It's very possible to have been coding 30+ years (and even find career success) now and still have a host of bad habits further amplified by an entitlement now fueled by a career of false assumptions of self competence.

In my experience the distribution of talented developers tends to be bimodal at all ages it's just the older ones stand out more because they should know better. Also as mentioned else where in the thread, the best developers build up network so they tend to self select out of bad deal start ups and the normal hiring processes so you're not even sampling randomly from the population if you're just doing open hiring.