Almost 4 year old not potty trained

I’m not trying to shame or be rude!!!! My aunt has a daughter who will be 4 in these coming up months who is not potty trained. I have always been the baby in the family, I never grew up with younger kids around. My grandma has made comments about her not being potty trained yet. Almost making it seem not normal. Is that not normal? Is she suppose to be potty trained already? My boyfriends mom has a 3 year old is who also barley starting to potty train. When is typically the age kids are potty trained? Again, not trying to be rude or anything I just genuinely am not very educated on the subject. I know every child is different.