Although I didn't give the article much credence, for reasons others here have stated, I must admit that, 12 years after stopping work, I have been descending into a retirement slump recently. Unlike the author of the article, it has nothing to do with money. I have no financial worries whatsoever. All my material needs, shelter, food, healthcare, etc are all taken care of. For most people, to be able to finance their life without having to lift a finger is a dream - it certainly was for me while I was working.
I'm ashamed to admit it, but I think my problem is partially a lack of interests, combined with an extreme introversion that isn't always good for me. After I stopped work, I was happy to spend a lot of time at home catching up on an old hobby of mine, ham radio. I spent several years building radio gear and blogging about it. I proved to myself that I could build to a higher standard than I had done in the past. It was all quite satisfying. Once I had proven to myself that I could do it, the interest gradually slipped away.
I also busied myself with another old hobby of mine, photography. Back in the early 2000's, I had revived the interest by getting into the then relatively new medium of digital photography. I found that I was capable of taking photos that were much better than I had when younger. In the first 10 years of my retirement, I got myself another camera that was much more tuned to my current interests and discovered, once again, that I was capable of working to a standard that I was happy with. Once I got to that point, my interest in continuing waned significantly.
For almost 15 years now, I have been very keen on the idea of having an RV or campervan. A couple of years ago, I got myself a cool old Airstream campervan. I spent a little time getting it set up the way I wanted it, and took some trips. The plan was to discover the great American West - and perhaps more of the country, if that went well. I did see some great countryside and beautiful vistas, but also felt while I was traveling, that there was no "there" there - or at least, not as much of it as I had hoped. After each trip, I was quite happy to return home.
I have spent a lot of time at home over the last 2 months, recovering from knee surgery. This forced lack of activity has pushed me over the edge into inactivity, to the point where it's hard to motivate myself to get up and go out some days. It doesn't take much to keep me happy but, at the same time, my need for stimulation is so low, that I can easily slip below that threshold and become bored for quite a long time before I'll realize it and admit it to myself. I am bored to the teeth with binge-watching mediocre shows on Netflix and Amazon!
So that's where I'm at, in a nutshell. I'm hoping to pull myself together soon and find new ways to find meaning and enjoyment in my retirement. I'm only 57, so that would be a lot of years to spend feeling unfulfilled, if I don't.