I sadly had an experience last year with older team members neither having the sage wisdom nor the flexibility to add value to a project, but they were kept on because of diversity reasons. The project was still delivered on time, on par with specs and within budget, but the older people were sent on paid leave after the first month of the project.

While it's a cliche to assume older (or younger) people are never going to work out in a team, it definitely happens a lot where outliers in the age range simply cannot do the work, whatever the reason. (and I'm not talking about not being qualified, that's usually not the problem)

On the other hand, with this anecdotal failure we have seen anecdotal successes as well; but knowing that older members can fail on a project due to what they self-describe as their age does actually happen in just the way people seem to fear; just not as often as they seem to think.