What's a Mentor?

The other day I was wondering what I should do with the rest of my life, and I thought, boy at this point it would be great to have a mentor.  But then I thought, what is a mentor, anyway?  Have I ever had one?  Have I ever been one?  I really don't know.  Do you?

I know I've had a lot of great advisors, but I take it that a mentor is not the same as an advisor.   Am I right about this?  A mentor does more than just respond with some advice when you send him/her an email saying, what judges should I apply to or what schools should I interview with or to what literary journal should I send this prose poem written in the voice of a just-neutered Abyssinian Blue kitten, doesn't he/she?  Is a mentor someone who plays a more active role in your life, who comes down to your office or calls you up without invitation to suggest that you pursue a Guggenheim and then offers to write a letter for you?  If that's what a mentor is, then I'd reiterate the earlier suggestion that I would like one.

Or am I too old?  How old can you be and still get a mentor?  (I turn 40 in a month.)  I suppose this turns on whether you're looking for a mentor in your own field rather than a new one.  So, I guess it would be a lot harder for me to find a legal academic mentor (though I'm sure I could use one) than it would be if I decided to scrap it all and go to med school, in which case I suppose even a much younger person than me could be my mentor, assuming that he or she was a successful doctor of some sort.  This raises a further question of whether there are different types of mentors: more general life mentors vs. mentors for specific goals or purposes.  How targeted can a mentor be?  Can I have a mentor who only helps me work on my omelette making?  I have a good friend who tells me that when he was learning how to drive back in high school, his driving instructor took a really active interest in teaching him and keeping him informed about the road conditions, even going so far as calling him one night to let him know that the roads were apparently covered by black ice.  This is exactly the kind of thing I'm looking for.  Which raises the final question: How does one go about applying for a mentor?  Can you get one on Craig's List?