I started when I was 3, on a Honda fourtrax 300 if I remember right.
But my dad would ride on the back of the atv and shift for me, because my legs couldn't reach the pegs lol.

I NEVER got to ride one of those youth atvs. I don't think they a hazard, when used with adult supervision, but I do think they are sort of pointless. I learned pretty well on a full sized atv with an adult on the back lol.

The first time I ever rode solo was when I was about 8 or 9 I think.