I was four when I started too, OP. I think the gross feelings are just because it was new and different and a little weird. I remember doing it at a classical music concert with my parents because I was so bored. I'm embarrassed about it now only because what if I'd been caught? Otherwise, who cares? Little kids do weird stuff because they don't know better.

Masturbation is great because you learn about your body's sexual responses and can tell your partner how best to pleasure you. It prevents misunderstandings and dissatisfaction in bed, which is really, really important in a relationship. Plus, it's really fun on your own. :)

So I don't feel gross about starting so young, or even about doing it in public that way. Please don't either. *hugs*