I had to learn cobol last year. Not hard if you have read lots of books from the 70s and 80s and have a strong background in algorithms. It is expensive and annoying to maintain these systems, but until there's a business case to replace the underlying application, he's safe
I recently meet a programmer in his 50s, still working on Cobol. Sure, you aren't gonna hire him, but do you think he has any worries about his job?