You have tangible proof of something that is simply legal by US federal labor law. The Age Discrimination In Employment Act only protects workers 40 and over. (State or local jurisdictions can differ, but few do.) The Equal Opportunity Commission may care morally but has no standing legally in this case.
More generally, discrimination protections for employment are much narrower than commonly assumed to be. Discrimination is legal by default and becomes illegal only when a specific law cites a specific protected class. Some characteristics that are perfectly legal to discriminate on because there is no US law protecting the class: age under 40, smoking, obesity, height, car you drive, method of commuting, sports team favoritism.
More generally, discrimination protections for employment are much narrower than commonly assumed to be. Discrimination is legal by default and becomes illegal only when a specific law cites a specific protected class. Some characteristics that are perfectly legal to discriminate on because there is no US law protecting the class: age under 40, smoking, obesity, height, car you drive, method of commuting, sports team favoritism.