This is a question that I am embarrassed to ask anyone for various reasons but I am really curious.

My DD (21 months) and I had a mom and her DD (3 years old) over yesterday. The 3 year old went over to a shape chart (that we had long discarded in the corner because DD learned shapes around 18 months) and started asking what the shapes were. My DD answered, including trapezoid, octagon, ect. The 3 year old didn't even know square or triangle. The 3 year old is smart, she just didn't know these. I didn't ask if the mom hadn't exposed her to shapes before because obviously that would have been rude.

My question is: can non-gifted kids learn the shapes, colors, letters, letter sounds when they are really little too but most are just not exposed to it? Or does it just take them longer to learn? It seems so easy for DD to learn things (after exposure just a few times) and I don't know why and can't understand why other kids (even older) don't know them. How can an entire year (kindergarden) be dedicated to learning this info? I can't tell/don't know if my DD is "gifted" or if I am just exposing her to materials other parents aren't. She is my only child so I don't have another child of mine to compare her to. My closest nephews to her (3 and 4 years old) don't know many things she does but I can't tell if they don't know it because they were never exposed to it or if this is stuff that is hard to learn. None of her friends are talking much but she is talking in 5-6+ word sentences but could she just be talking so much because she loves me reading to her and we read so often? She is obsessed with space and knows all of the planets and talks about things orbiting (including her food that she "orbits" around her placemat), and constellations and wants to draw lines to stars to connect them and make constellations. She loves new words (her current being "fiasco" from a Fancy Nancy book. Can other toddlers learn these things but they just can't speak as well so no one knows? Or could they learn it if they were exposed to it and they just aren't? If kids can learn things so young and it is so easy for them to learn it, why aren't these things taught when they are younger?
DD learned the shapes, colors, letters (in order), letter sounds, counting, ect. before or around 18 months. She learned the body parts so young and seemed bored so my housekeepers daughter taught them all to her in Spanish. My mother was with DD at a hotel (when DD was 20 months) and a older kid was playing with her. The kids ended up realizing she knew Spanish and started asking her questions. DD replied (they asked her where her head was in Spanish) and corrected their pronunciation.
Can all kids learn this so young but they just are not exposed to it? I am seriously wondering. I don't mind if DD is not considered "gifted" but I really want to know why other kids don't know these things so young. Does my DD learn things quicker and absorb more, or is it just that she is exposed to these things that other kids aren't? Can other kids learn this stuff too and they are just not exposed to it?