Unfortunately technology is unlike some professions like, say, warehouse management or construction where techniques evolve with time, but there are more commonalities from one decade to the next. Technology sees highly disruptive change and so I would still argue that without keeping current in your knowledge, your experience has a very short half-life.
Incidentally, what you call "microservices on AWS" is architecturally identical to how mainframes worked in the 1970s, you would do it with CICS. Much of the computer science, algorithms and datastructures, in every day use, were discovered in the 70s if not before. So either you have very limited experience of technology, or this is just ageism.
As for me, I've run AS/400 shops (back when it was the AS400, but we did use newfangled 5250 emulators), been responsible for development in companies implementing highly distributed client/server based products, and most recently I've been involved in developing back end systems for web and iPhone applications (and, yes, on AWS in microservicey ways). I've been around technology plenty. I can tell you, too, that my early mistakes with AWS were precisely because I allowed my prior monolithic systems experience take too much precedence in my judgments when I first approached it. It was not the same. I needed to learn the new lessons; perhaps my only advantage was I recognized it quickly and recovered.
It's not ageism, however, but a realism that recognizes that not all experience is the same or applicable to every situation: it takes continuous professional development to make that experience worth a shit. However, I can understand why you'd be a little overly defensive in your response however... being a developer of a certain age. Don't worry. I'm about the same age as you, as are many of my colleagues, and I don't think we're too worried about finding work.
1) That's not a threat, if you think it is then call the Internet Police - they have a hashtag #hnwatch just for that
2) He is simply wrong that experience doesn't carry forwards. To use my Amazon example, the value in that business is understanding how people buy books and how a logistics operation to deliver them works. I don't know what technology Amazon actually uses in their warehouses but it's nothing that couldn't be done with terminals and line printers, I'll bet dollars to donuts, and nothing that would be unfamiliar to anyone working in the logistics field in the 70s.