In the military, a pilot usually has to complete a full flying tour before getting an instructor's course. One tour is around 3 years and 1000 hours - and a bag of experience that somebody straight out of a licence test doesn't have.
The RAAF tried once, sending a newly-winged pilot straight to instructor's course, but it wasn't worth doing a second time - don't know the official reason, but the unofficial one was that he had no credibility amongst the other instructors.
I know that when I went through training, all my instructors were Vietnam vets who could pass on a lot of knowledge. (It didn't sink into me, of course.....)
