You are spot on that it is very difficult to keep up with the languages needed to know (and also other skills in the IT industry). And the technology changes faster now than ever before. I believe we need to acknowledge that it is impossible to keep up with everything, and the best one can do is constantly spend some time trying to learn new skills (and hoping you have picked the right new skills). I've always belived that if you know one programming language well, you can adapt more easily to a new language. Unfortunately not all employers get this, and the "HR filter" certainly does not. I think it is very admirable that you will spend time teaching the younger generation what you have learned.