Hi, my name is Pepper, and I'm a squirter.
This is a new phenomenon for me, and for me, it wasn't something I could (or can) control, and it is not an all the time thing. Thank goodness. Quite frankly, it's a pain in the butt, because you have to change the bed before you can go to sleep. But, once you know the combination, it springs the lock, so to speak.
I don't know percentages, but I bet every woman can squirt. They just haven't had the right stimulation for it, and aren't relaxed enough to do it.
Pepper