It's an interesting question, but the article doesn't try to differentiate between a dearth of older developers vs. a dearth of older developers sending resumes to Hibernating Rhinos in Hadera, Israel. Like, are they affected by local demographics, their own corporate culture, the ways in which they do recruiting, etc.
It seems like the article is written from the perspective of assuming that the age distribution of the job seekers that they interview is equivalent to a random sampling of all software developers worldwide, but it could also just be a function of how resumes make their way their way to this particular company in this particular part of the world via the particular channels through they receive resumes.
I would still expect a random sampling of people looking for programming jobs worldwide to be heavily weighted towards recent grads however, for lots of reasons:
(1) Just in terms of numbers, there are a lot more people with recent CS degrees than degrees from 20+ years ago.
(2) People in the first few years of their career are much, much more likely to send resumes to a gazillion different places. They are also much more likely to start looking for a new job after 1-2 years.
(3) People with less experience are much more likely to apply for an entry-level position.
(4) If you have a company mostly or entirely staffed by people in their 20s, that by itself is going to scare off older developers and encourage younger developers to apply.
(5) If most of the company is composed of people in their 20s, then most of the resumes you receive from acquaintances of your existing employees are going to be from people in the same age group. So, there can also be an element of it being a self-perpetuating thing.
Etc. etc. etc. Basically, why there are fewer older developers is an interesting question with multiple answers, and why this particular company doesn't get resumes from them is also probably an interesting question with multiple answers. The questions raised by the article are so general, however, that there are no simple answers.