Weapons systems are designed to be maintained in the first echelon rear support area. That means you build it to be able to work for expected campaign duration with skilled maintenance available between sorties. The piston driven bombers of World War two were built to the same sort of standards. Had they been more reliable, they would have been challenged by more stressful missions.
Modern Aircraft are incredibly complex, and yet reliable enough to survive high intensity use in quick rotation in and out of combat operations. Without intense support facilities (far more extensive than was expected in WWII) close to the theater of operations, they are almost useless. But the system includes the availability of such maintenance. So the answer, if you get one, is not really all that applicable to the real world. A modern jet, without an expert and fully equipped maintenance crew, could probably only run a half dozen combat missions at best. But working off an aircraft carrier, they routinely fly twice daily missions for weeks at a time and less intense schedules for many months.
The elder bomber was less finicky, and could be used without such intense support. So, no such support was provided. Twice daily missions would probably involve regular maintenance losses. Months of daily bombing runs would do the same.
By the way, B-52 bombers are all older than their pilots.
“No flying machine will ever fly from New York to Paris … [because] no known motor can run at the requisite speed for four days without stopping.” ~ Orville Wright ~