There may be also significant variation in size between people today. Everlasting breast development throughout puberty is because of estrogens along with The expansion hormone. Female individuals are the only mammals that completely establish breasts at puberty; all other mammals produce their mammary tissue through the latter duration of pregnancy. https://grok.com/share/c2hhcmQtMw%3D%3D_5ad6450c-533d-442c-a09c-9f7bce1babfb