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.