When does puberty start?

Variable: Girls generally start between ages 8-11 and boys between 9 and 12. For girls the first sign is a growth spurt and then development of pubic hair and breasts. For boys puberty generally starts with an increase in testicular size and their growth spurt comes later. Menses generally starts about when a girl's growth spurt is done.

The brain decides: Puberty is a complex interaction between brain signals, hormone producing glands & the tissues of the body. In girls it is heralded by growth in spongy breast tissue below the nipple on one or both sides. In males, the testis begin enlarge. Genital and axillary hair are more dependent on the adrenal glands & baseline hormone production that can precede the other hormones by a few years.