I know that lots of elderly people squirt when they sneeze or cough...maybe that's the problem. You are just too damn young!
Something to look forward to, though!
Seriously, all women are different. I don't do any pushing or fancy muscle contractions in order to squirt. I have to be relaxed around, and comfortable with, the gentleman I am with. I also need simultaneous clit and g-spot stimulation for it to happen. If any of those things are missing, it won't happen. It doesn't happen if I 'try', only when I am comfortable enough to really let my mind go, if that makes sense. I have never been able to squirt on command and am a bit skeptical of those who can, but I suppose anything is possible..