Yes, belonging more and more to this age cohort the SotT article caught my attention as well and I welcome a discussion about it.
Anecdotal evidence will get you only so far, but I have to say from personal experience that I've encountered far more examples of smart, lively and up-to-date old age people than I did those who approximate the conventional stereotype -- but that's just me. I didn't frequently visit old folks homes where people are stored like empty bottles in a crate with almost nothing else to do than just vegetate along; so I might be sort of biased, I think.
Being almost 69 yo, I may be still just too young to experience any steep decline and I certainly did notice over time some slowing down of physiological and motor functions about which I recall a recent post of Laura stating something similar -- but that's it! No withering nor dithering in cognitive and related functions as of yet. Actually, I surprised myself more or less in recent years by being able to get up-to-speed in reasonable time frames with not only computer tech, security and software but also with quite a lot of subjects discussed on this forum, of which I knew next to nothing when I started with them. There are some failures too in this respect, of topics beyond my current reach but that's mainly because of a completely lacking basic knowledge about never before encountered subject matter -- which obviously isn't remedied that easily, but within reason I'm working on those as well or at least trying to do so.
This doesn't prove anything, of course, and I'm aware of that. Nevertheless, I always had the same conviction about the elderly as these articles propagate.
The real problem lies elsewhere, IMO: finding meaningful things to set your teeth into and pursuing your interests on whichever subject to the full. In short: to keep busy with worthwhile things. The more you try to take on new endeavors and persevere with them when the going gets a little tedious or nitty gritty, the better you are able to maintain and expand your knowledge base and keep it as current as possible.
At least, that's my take on this at the moment.