We still had NCO Pilots and Navigators in the late 60's, some of whom were still in their 20's.
The original decision that aircrew should be at least of SNCO status was made on the grounds that they would operate over enemy territory and were liable to be captured if shot down.
Those prisoners of JNCO rank or lower can be put to work under the Geneva Convention. SNCO's can only be made to supervise.