@Dominions SonBeginning puberty at 12 or 13 is completely normal.
From the Cleveland Clinic:
The 5 stages of puberty
Girls generally begin and end puberty about two years earlier than boys, starting around age 11 and ending around age 16.
However, African-American and Hispanic girls tend to start puberty earlier than Caucasian girls, notes Dr. Issac.
The Tanner Stages break down the changes of puberty in girls as well as boys:
Stage 1. In this prepubescent stage, no changes have occurred.
Stage 2. Between ages 8 and 13, girls typically experience the following:
The breasts begin to bud, and the areola (pigmented area around the nipple) enlarges.
Light genital hair appears.
Height increases by about 2¾ inches per year.
Stage 3. As girls move through this stage, typically between ages 9½ and 14:
The breasts continue budding.
Pubic and underarm hair begins to grow. Genital hair darkens, coarsens and covers more of the genitals.
A growth spurt of more than 3 inches per year occurs.
The skin becomes oilier, and acne develops.
Stage 4. As girls go through this stage, usually between ages 10½ and 15:
The breasts continue to grow, and the nipples start to protrude.
Body hair reaches adult levels.
Growth may continue at the rate of about 2 ¾ inches per year.
Problems with acne may continue.
Periods typically start around age 13 (usually around the same age their mothers' periods began). Some girls, especially those lacking body fat, start later.
Stage 5. Development typically ends.
In this stage, girls reach physical adulthood. Most attain their peak height by age 16.