Short answers, pulled from the story.
Females initiate physical puberty at an average age of 10½ years, and the first sign is thelarche, which is a firm, tender lump under the areola of one or both breasts. This breast development typically occurs around age 10½ and marks the beginning of the physical transformation. The internal neurohormonal process begins one to two years before these visible changes appear.
Males begin their physical puberty journey between ages 11½ and 12, and the first sign is gonadarche, which is the enlargement of the testicles and scrotum. Testicular size averages 2 to 3 centimeters in length before puberty and rapidly expands to adult volumes of 20 milliliters or more. This process continues to grow for approximately six years after the initial signs appear.
Menarche, the onset of menstruation, occurs on average around age 12½ and typically happens about two years after the first breast development begins. In the first year after menarche, about 80% of cycles are anovulatory, meaning ovulation does not occur, and this figure drops to 50% by the third year. The uterus, ovaries, and follicles increase in size during the two years following thelarche.
Obesity has been linked to an earlier onset of puberty in females, with early obesity cited as a cause for breast development before age 9 and menarche before age 12. The body fat percentage increases to a greater degree in females, contributing to the typical female distribution of fat in the breasts, hips, buttocks, and thighs. Severe environmental conditions such as poverty and poor nutrition can delay the onset of puberty.
Females who enter puberty early often experience negative outcomes, including lower self-esteem, depression, and a negative body image due to the social pressure to be thin. These early-maturing girls may develop relationships with older people, increasing the risk of alcohol and drug use, unprotected sexual relations, and eating disorders. In contrast, females with a later onset of puberty generally exhibit positive behaviors in adolescence that continue into adulthood.
The average age at which puberty begins has dropped significantly since the 1840s, with historical data from the 19th century showing an average age of 15 for females and 17 for males. A 2006 study in Denmark found that puberty, as evidenced by breast development, started at an average age of 9 years and 10 months, a year earlier than when a similar study was done in 1991. This phenomenon could be linked to obesity or exposure to chemicals in the food chain.