For me personally? I would try not to discriminate, and just evaluate the individual's skillsets as they fit the job. I have a lot of confidence in my ability to do this, but I suspect that's sort of the point: there's a range of ability when it comes to assessing candidates, and generally speaking no one believes they're terrible at it; they believe they're doing a good job, and of course, many are not.
WRT the "older candidate stereotype," I think that's a bit more of a grey area. Are people in their late 30s and 40s being passed over? There's not really any mental decline at those ages, and I would suspect that the other issues discussed (ie, we can pay a younger candidate less) are the true issue. For sure, mental decline is a real thing, but it varies quite a bit in people. If someone were in their 50s and 60s, I would definitely be alert to the possibility of decline and outdated skillsets, but I would also be attentive to the fact that this is not necessarily the case. Does this make me bigoted? I'm not sure, and I think this is where the grey area lies. It's certainly not unusual for someone in their 60s to have lost a step compared to when they were in their 30s. It's hard for me to imagine that the stereotype should carry _no_ weight in that case.
The ideal would _always_ be to evaluate the person on an individual basis. And from a personal perspective, this is always what I would strive to do. (ie, I was talking about stereotypes in the general sense, not necessarily as they applied to me.) But people take mental shortcuts. Somewhere out there is a case where the 31 year old was the correct hire over the 62 year old, with age being one of the major factors. Is this stereotype overly-relied on? Is it just a stand-in for bad business practices? (ie, we can pay younger people less) I'm sure that's true sometime.
Realistically, people will be making mental shortcuts as they navigate the world. There seems to be no escaping this as a general fact. People often misjudge me, but this is seldom due to any protected group status. The idea behind the "protected groups" is that there has been pernicious, malicious, and egregious negative judgement aimed at these individuals. I personally find that racism or sexism feel qualitatively different than something like ageism.
The real trick, at least in my mind, seems to be to be able to see the individual in front of you rather than the group. It's just that there are two problems with this:
- People are not always very good at seeing the individual rather than the group.
- Seeing the individual rather than the group will not necessarily move representation numbers if stereotypes are based on fact. (as an easy example, there are not very many people in their 60s playing professional football. You don't need to be "bigoted" against older people to arrive at this scenario. You could arrive here with purely objective fitness tests.) And crucially, many people see "incorrect" representation numbers as proof of bigotry.