what is the age of onset of puberty dropping among american girls
1 A new study finds girls are developing breasts earlier than ever before; American boys and girls are entering puberty about five years younger than they did in 1920.
Girls usually complete puberty by ages 15â17, while boys usually complete puberty by ages 16â17. The major landmark of puberty for females is menarche, the onset of menstruation, which occurs on average between ages 12â13; for males, it is the first ejaculation, which occurs on average at age 13.he average age at which the onset of puberty occurs has dropped significantly since the 1840s. This was dubbed 'the secular trend' by J. M. Tanner. In every decade from 1840 to 1950 there was a drop of four months in the average age of menarche among Western European females.