While he may not pass the exams which are an arbitrary measurement, every time he tries again he will have learned something new, even if it will not help him pass the test. While he is studying he is with young minds. They can show him how they change as they grow. Maybe he was never meant to be in the army.

He has it right, never ever give up. It may take him a thousand time, but sooner or later by accedent he will pass.

he should just stick to husbandry instead of wasting time & money on fruitless effort

If the exam was for persistence he would get 100%, never stop trying.