With reasonable intelligence yeah. I've met 7 year olds that speak perfectly, albeit with limited vocabularies. :B
they must be some smartasses if they can master grammar at the age of 7, hell but seriously
Japanese is different enough from english as it is, now grammar + english is a hell of alot harder than that.
and besides that point, most females i know don't tend to even USE grammar.
either way this is hardcore evidence that either stocking has an IQ of 200+
or it's lying about its story and is just an english weeaboo