I had a mentor.  He was my band instructor from High School.  He spent a lot of time working with me on jazz improvization, supported my desire to work on other instruments, got me hooked up with a Jazz Combo with players WAY older than me and pushed me to raise my standards.  I hope he's doing well.

As a guitar instructor in my very spare time (I have only two students) I only take beginners and I look for kids who might not have any other resources for instruction.  I use a book called Zen Guitar by Phil Soto which talks as much about discipline and a healthy attitude as it does about playing.  Phil, unfortunately passed away a few years ago but the lessons of his text are applicable with any instrument or any setting in life. 

PRH