Ageism in the software industry: is it even rational?
medium.com
medium.com
Senior people are more expensive, companies see programmers as a utility and don't want to pay 5x for a senior code monkey while they can pay 0.5x for a junior code monkey, period.
It is more often a cultural thing when 20-somethings working on their startup don't want a daddy to hang around with them. Corporations with strictly formal hiring procedures are usually less ageist.