My grandfather had gotten me into the whole tinkering thing when I was like 8. I had a go-kart that I would mess with, and he had an infinite supply of crap that I could take apart, and weld on, and that sort of thing. When it wasn't my go-kart I was messing with, it was my 64 Galaxie 500 (which I still have), or the quad. I miss those days.
I realized later that, anyone in the world can read a Haynes or Chilton's manual, and can fix some problems on a car. It's just like reading the instruction sheets that come with Lego's to make something. To be able to call yourself a Mechanic, you need to know how to pull your ass out of something you messed up. That, and you need to know how to use certain exotic tools in the right way.