As someone whose done a lot of hiring (at several companies), senior devs with a lot of (applicable) experience can always find work even if they’re “old” (40/50/60+).

But career changers will have a rough time - e.g. I remember a social worker who went back to school in his late 30s looking for an internship(as a developer), he had a much harder time getting hired than someone in the same position in their early 20s.