I quite like this paper. Does a great job laying out scientific support for things we already "knew" in our guts - like having retirement ages at around 65, for instance, being an ideal milestone to start transitioning folks from leading hard work to supporting activities.
Where I worry is that these papers will be used to justify ageism. Looking through these comments, there's quite a lot of positions being bandied around that I've heard justify some truly atrocious hiring/firing decisions before, and we need to be cognizant of the reality that age alone is not an indicator of success or failure for a given role or task. It's helpful to keep looking into this, but we also need to be aware of our own biases.
I don't know that people are really looking for things to justify their ageism, just like I don't feel that racists are actually trying to justify their view.
As a seasoned citizen myself (55), what I've experienced is that ageism seems to be more about having common points of view and cultural references. It is similar to how several studies show that people tend to hire others just like themselves despite actual credentials. This is the challenge with age, race, culture, and even sex.
I do like that this paper shows that I will be just coming off my peak of power at 65 and that all I need to know is what 6-7 means so I can talk to my younger colleagues. :)