I'm not sure why you're being downvoted. I'm fairly sure this is the correct reasoning. We generally think it's acceptable to discriminate on the basis of ag

I'm not sure why you're being downvoted. I'm fairly sure this is the correct reasoning. We generally think it's acceptable to discriminate on the basis of age in many contexts, one of the most important of those being experience. If you are selecting candidates with more experience or "maturity" than is possible for someone of a particular age, you are effectively discriminating by age. Perhaps people have morphed their internal definition of the word "discrimination" into something that differs from the dictionary and therein lies the objection?