Since World War II, the U.S. Air Force, along with American naval aviation, have become the dominant air power on the planet. Moreover, the availability of nuclear weapons has restrained the major world powers from fighting each other directly. So the only wars are between second and third rate proxies, versus American fighter pilots. These smaller nations tend to see their air forces destroyed on the ground, or have too few aircraft in the air to allow American pilots to become aces. The biggest threat to American pilots is anti-aircraft fire, either bullets or missiles.
The future of air combat is in unmanned aircraft, including robotic fighters that no human pilot could overcome. This is because the unmanned aircraft can undertake maneuvers that the human body cannot handle. Too tight a turn at too high a speed causes human pilots to black out. Robotic aircraft do not have this problem. Moreover, a robotic aircraft would be run by software, that could possess a better degree of situational awareness than any human pilot. This isnt science fiction, as many current warplanes have many of their functions run by computers. This is often done because a human simply could not make flight decisions, and execute them, fast enough to prevent the aircraft from crashing. Braking systems on many automobiles use the same technology. Its not a revolution in technology that is creating the robotic fighter, but an evolution. The ace is becoming extinct.
In the last half century, only three U.S. Air Force pilots have become aces (destroying five or more enemy aircraft.) There may never be any more aces. In nearly a century of operations, only 816 American air force fighter pilots have become aces. Most (87 percent) of those were in World War II. There were 39 aces in the Korean war, and only three during the Vietnam war. In the last ten years, seven pilots scored two victories, and three shot down three aircraft. None scored four or more victories.