You highlight another good point, in that ageism is just a symptom of a broader psychological phenomena of "othering" others. I suspect that even if I was indeed younger than my manager, simply having a child and entering a new life stage with newer, more important priorities caused me to be treated differently. In a way I think the manager just wanted people who are just like them because they were a lazy manager, and wanted an easy way to relate to others rather than the hard work of understanding other perspectives and experiences. A ton of companies I have worked for preached diversity of thought, opinion, and background, to the wazoo and very rarely have they practiced what they preached.