On the other hand I had young instructors who were fantastic, motivating and very well prepared both in the air and in the theory (even if just passing thru, waiting for an airline job), and older retired airline Captains or ex-RAF types who were indeed very experienced but not very good at instructing and rather unfriendly.
Got to remember that military and line training instructors teach people that have already been thru a selection process. It's much harder teaching a man off the street, with no particular talent or aptitude.
So a 12000 hours fast jet instructor does not necessarily make a good PPL instructor.
Ivor