Breast Development. Girls usually begin puberty between the ages of 8 and 13 years old. Uneven breast growth and soreness are both totally normal and usually improve with time. . Information: Stages of Adolescence.
Breast development happens in certain stages during a woman's life: first before birth, and again at puberty and later during the childbearing years. Changes.
Breast development, or the growth of a girl's breasts, is often the first sign of is slight swelling under the nipple, a stage of development called breast buds.