The generalisation that the best instructors are the old silver haired foxes is too big in my opinion.
This from someone who has instructed amongst a wide range of professionals: You won't hear this notion bandied about very often, infact it's positively ignored amongst those in the know, but most of the old boys look for ways out of getting airbourne (unless they're part-timers flying for fun) because (to put it bluntly) 10'000+ hours sitting in a spamcan makes one either very peculiar or extremely impatient.
Faced with the prospect of a young, hungry and enthusiastic instructor or the hackneyed old goat with a drink problem, I know who I'd sooner be learning to fly with, I see students make that same choice every week and they don't chose the old git! You make generalisations? I can play that game too... but I'm not far off the mark you know - which might scare some people should they ever choose to remove their rose tinted specs. Things are not always as they appear when you first experience GA as a student pilot - trust me!
Happy flying!
VFE.