There exists also substantial variation in sizing amongst people. Lasting breast development all through puberty is due to estrogens in conjunction with the growth hormone. Woman people are the only mammals that forever develop breasts at puberty; all other mammals acquire their mammary tissue over the latter period of pregnancy. https://grok.com/share/c2hhcmQtMw%3D%3D_5ad6450c-533d-442c-a09c-9f7bce1babfb