I'm not really sure how likely that is, because it happens in some non-english countries too.
In my country "I" is not the first person singular personal pronoun, so that reasoning is far fetched.
I always thought it was because you learn to write neatly in lower school, and the dot can become either untidy (e.g. more of a dash), or hard to see. So I think to make a nice dot some start to draw a tiny circle, that eventually grows out to a big thing. Back in the day (talking about 15-20 years back when I was in lower school), we used these ink pens and making a dot could actually spray out the ink somewhat, and spatter your paper. A small circle was one way to work around that issue.
Why girls? Because they tend (at least from what I remember) to be more invested in a neat handwriting, they take pride in it.
I personally hate it