In my experience...
No, I can't really control it. Gradually, as the years have gone by since I started squirting, it happens more and more and I have less control.
The only way to really control it is to intentionally refrain from g-spot orgasms -- and even that doesn't always work.
However, that being said, I wouldn't trade it. I feel kind of short changed if I don't have a squirting orgasm these day. They're so much more intense for me.