We could argue all day about the intent of the US law, but the wording of the law lists protected classes and older workers is a protected class, and younger workers is not - discriminating against older workers purely on the basis of age is illegal and discriminating against younger workers is legal. The article clearly states the case is tried in San Francisco so US law is the only relevant law.

I agree with your sentiment that no age discrimination is btter unless that is somehow relevant to the job.