From infancy to puberty there is little change in the reproductive system. During puberty individuals become sexually mature. Timing for development is different for every individual but the release of GnRH from the hypothalamus, LH and FSH from the anterior pituitary and either testosterone or estrogen from the gonads contribute to the maturation of the reproductive system and development of secondary sex characteristics. The hypothalamus begins producing GnRH around age 8 or 9, leading to the pre-puberty changes. The average onset of menstruation for girls is 12–13 years old, and the average age of fertile ejaculations for boys is between 13–15 years old.