What Causes Wrinkled Skin On Neck And Stomach?

hey doctor, i have been to a few dermatologist and none of them can figure what is going on... the only they can tell me is i might have elastosis and i was wonder if there is anything i can do for it. I'm only 18 and my neck and stomach looks like a grannys. i have never been heavy so i dont know why it is like that.