Unfortunately no real mentors that I fish with... And I am famous for learning things the hard way!
But, Jay and Randy at Rocky mountain anglers have given me countless small valuable pointers that have helped me improve. When I started out, I stopped in to buy some flies. I was overwhelmed with "try PMDs, BWOs, some PTs, Barr emergers, and maybe some princes."
I had to admit that he "could have basically been speaking Chinese to me" and that I had no clue what he was talking about. Jay picked me out a few, gave me a few tips, and I started catching fish. I later found out he is a published author, pro guide, pro fly tier, etc. Never would have guessed because he is just a nice guy that was helping a complete novice! Climbing is the same way, the 'Best' of the pros don't care if you suck as long as you love what you are doing. To me that is the best attitude. Better to help someone not suck than to laugh at them sucking/abusing fish.
One afternoon fishing the 'toilet bowl', I received a ton of help on fighting bigger fish more effectively from a guy that was willing to share the sweet spot. Amazing what one afternoon with someone more experienced will do.
I've gotta say, this site and its members act as mentors. I've learned so much more about casting, presentation, and gear since visiting this site.
Thanks again to the veterans for sharing so much valuable information
with those of us who are still 'falling in love' with the art of fly fishing.