I started the violin when I was three.  I came home from day care one day and told my mom that I wanted to play a guitar with a stick.  Took them a while to figure out what I meant.  My parents think I saw it on Sesame Street, but who knows.
 
I played up until college and did a couple quarters in the orchestra.  I think I went into book 5 (I never put a lot of time into it, so it took me a while to progress), but it opened up windows to other instraments.  In high school, I taught myself the flute, saxophone, trumpet, clarinet, and dabbled a bit with a trombone and the piano, but not much.
 
I grew up with the Suzuki method and your teacher makes all the difference.  If personalities don't match, then learning will be a drag.
 
For learning third position, it may help to put a small dot sticker where your third finger goes on A in the first position.  You can use that as a visual guide to where your first finger needs to go in the third position until your fingers/wrist know what they are supposed to do.