When I had my first kid, I was pretty surprised how early she started "pretending". Before my daughter could say more then a few words, before her motor skills were developed enough to do more then pick up and drop small her toys, etc. she was already moving her toys around like they were real animals, pretending to feed them, etc. She couldnt have had much understanding of the real world before she started making an imagined one.
My kids have not done that. Which leads me to question: did adults mimic pretend play like that with her when they were socializing with her? I have seen adults do it in front of kids as attempts to interact with them. But we did not done that and our kids have not done that until much later.
Starting somewhat earlier, she also mimicked adults pretending, we'd pretend to talk into her toy phone for example, and then she'd do the same. I think in those cases, it was pretty clear she was just mimicking, not pretending.
The play with dolls seems more explicitly pretend though. I dont think she saw adults to it first (though once she started, they definately joined in and reinforced the behavior though). She's still mimicking our behaviors, trying to feed the doll like we feed her, etc. But she uses toy bottles to do so, not the real ones, and she doesn't try to feed other real babies when she encounters them.
I suspect explicit mimicking and pretend play are something of a spectrum. We start trying to exactly copy the adult behavior around us, and then start abstracting bits.
