Yes, some people have chests that flat. I know many ciswomen who are flatter than a box of crackers, and most breast tissue is FAT not glands. Nipple size is mainly due to skin stretching from bigger chest tissue. I got lipo top surgery with glands cut out, NO skin removal, and my nipples dramatically shrank. I am only 8 weeks out!! If he was an A cup before then yes he could have a chest like that. Look at that person, they have no body fat. A female that thin who has never been heavier would not menstruate nor would breasts develop so yes it is possible.