It isn't the military. You can't chop somebody.
There are difficult cases and there are methods to teach them.
Prehaps the chap with the NPPL needs some goodground school, to help him overcome his fear. When he understands what is going on he may progress further.
After all flying the aircraft should be the last part of the lesson. All too often people are too keen to get flying. This is partly to do with the short lesson allocation and also to do with instructor ability.
I know an instuctor, (who rebuilt my flying skills) who managed to get a chap with severe learning difficulties to do his first solo.
I am happy to pass his details over to you.
I fly with him as often as possible to help polish my skills and improve my patter.
You are never to old to learn.