That's because women's breasts have a similar amount of glandular tissue no matter what their size. You can't change your breast size by diet or exercise. The first sign of puberty in most girls is breast development. This usually occurs between ages 8 and 13, but may occur as early as 6 in black girls and 7 in white girls. Some girls skip stage four while others remain in stage four.
Most girls are at stage four when they have their first period.
One breast may start developing before the other. One breast may develop faster or more than the other. This can usually be hidden with loose shirts or bra padding. A nodular or lumpy breast texture is normal in adolescents. Breasts swell during pregnancy and breast-feeding.