If somebody is older, then you probably DO have to pay them more than if they were younger, because older candidates likely have more experience and have correspondingly higher salary expectations.

So there's that. Now suppose you have an older candidate who is not demanding high seniority pay. In that case they should be on equal footing with the younger candidates, right? Well, no. There's the double standard of "if you're so old, why aren't you above our pay grade? Shouldn't you be a manager or something?" That I don't know how to fix. Then there is the more overtly discriminatory "I'd rather hire the young candidate because old people are slow." Maybe what it really comes down to is "I don't want to work with my dad."