All the dudes in Iron Maiden are between the ages of 59 and 66. So still pretty young, but at some point they're going to release their final album, do one last tour, and call it quits so they can happily retire (and it doesn't become sad to see them live). Fortunately 2015's The Book Of Souls is probably not the final album.
According to bassist Steve Harris in an interview with Metal Hammer, he's "pretty damn sure we will do another album." He also adds that the band has been talking about hanging it up for quite some time now, and while that slowly becomes a more realistic option, it's not happening right now.
"We've got this [touring] cycle going on. I'm pretty damn sure we will do another album, and then all well and good, we'll go out on tour to back that up. How long that will go on for, I don't know. We've been talking about this kind of thing for the last 20 years, but as time goes on, it becomes more of a reality that one day we may not be able to tour any more. But I don't want to think about that. You've got to enjoy the moment."
So there you have it. There will probably be Iron Maiden #17 at some point.