I think squirting does have to do with anatomy. Some squirt all the time while for others it is hard to do it. I think the reason for it could be difference in women of the actual G-spot location.
I am 28, first time I really squirted a lot when I was 25 and was really drunk. Then I squirted again with 27 when again I was really drunk, drunk to the extend where you don't feel any pain anymore. Both times when I squirted was by manual stimulation by my husband.
Then I got pregnant. With the pregnancy there are a lots of changes in pelvic floor muscles. So during the pregnancy itself I had troubles with my pelvic floor musclutare, however I would squirt everytime I would masturbate, while stimulating my clit, no vaginal insertion at all. And usually I would squirt before coming. First I was just wondering about the mess, but then I realised that I would squirt. I figured that the uterus pushed down on the g-spot and that pressure made me squirt without any effort. After the pregnancy it became much easier for me to have a g-spot orgasm, and squirting itself happens only if I have a buzz (but don't need to be completely drunk anymore). And as many say that women tend to squirt easier when they age, I think it must be related to the fact that when we age our pelvic floor musculature weakens, and maybe that way the g-spot becomes easier to access.
Also interesting that the squirting actually happens before the orgasm, at least with me. And I am really wondering what alcohol has to do with the squirting, does that make relax your mind or your muscles? Wish there would be more info on that online, any feedbacks on my theory are appreciated.