Breast hypertrophy (excessive breast tissue) is a fairly common problem that affects one physically, mentally, and emotionally. As both women and men develop breast buds, they are affected by the amount of estrogen production or the estrogen-testosterone balance as puberty advances. The other factor in breast tissue development is its responsiveness to that estrogen, which is hereditarily dictated. When breast development usually begins, the breast buds respond to the estrogen and have an increased deposit of fat and fibrous tissue to increase their size. If a person is hereditarily predisposed to large breast development, this usually starts at age 11 to 13 and continues through the mid to late teens.