I was researching the possibility of an ageism lawsuit, and ran into this article. It's a good read, if somewhat discouraging.
https://www.nytimes.com/2017/08/07/business/dealbook/shown-the-door-older-workers-find-bias-hard-to-prove.html?mcubz=0
One of the points from the article:
And a 2009 Supreme Court ruling has made proving age discrimination more difficult legally. In a case brought by the insurance executive Jack Gross, who was among a dozen employees who were demoted, the court overturned an initial ruling favorable to him and imposed a tougher legal standard.