Over the years I've done a lot of work at my kids preschool as they have gone through so we're talking kids that are just 3 up to 5.5yrs and when they have done drawing of people, often it is the girls that seem to master this earlier and better than boys. At the start of each year they have to do a picture for their keepsake folders of "Me at my first day of Preschool 2009" etc and there are easily more girls than boys that can draw an actual person. This includes both the 3yo class and the 4yo class. I have no idea why that is though and it is purely anecdotal, but still interesting none the less. I know with my own kids that DS1 and the girls could draw quite early, but DS2 who is 3 in 4 weeks is no where near drawing anything recognisable.
I found this link that might give some people and idea as well
Drawing Development in Children
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