Extra loose skin baby

How normal is it for your first baby in your 20’s to have extra loose skin? I’m 23 and had my first baby and he’s 10 months but I still have loose skin that seems to not be going away. My cousin just had a baby too and she has no extra skin and same with my sister. We are all the same age to -well around the same age in the 20’s. I don’t get it because I was a very small girl and skinny before my son & now I’m 150’s with some extra belly. I don’t mind my weight but my belly bothers me and makes me insecure and more insecure that they don’t have nothing and back to their regular size but I have extra skin and so many stretch marks:(