It depends on what you're working on. I'm in the simulation area at an engineering company, and we've got plenty of Fortran code that dates back to the '70s that's still just fine. A little maintenance to work on removing deprecated syntax, a little work to replace common blocks with a more decoupled design, and we're probably good for decades more use. And if we can't get to that maintenance work right now, the strong backwards-compatibility of Fortran will have our back until the next opportunity. :)