SternisheFan writes: "Boys in the US are hitting puberty as much as two years earlier than in previous decades, according to a new study out Saturday from the American Academy of Pediatrics. The study suggests a well-documented trend seeing girls hit adolescence earlier than their historic counterparts has been mirrored among boys. However, the authors said the causes of change, or what it could mean for public health, remain unclear. African-American boys were generally the earliest to start puberty, with boys as young as nine years old showing signs of maturation, according to data on more than 4,000 boys in 41 states, provided by their pediatricians' offices. Non-Hispanic whites were next, with the average age of puberty onset coming at just over 10 years old, while Hispanic boys hit puberty on average a few months later, at just under 10 and a half. The ages were calculated based on when the pediatricians saw "stage two genital and pubic hair growth." "Following changes in growth and development is an important part of assessing the health of the nation's children," said study author Marcia Herman-Giddens in a statement. But this kind of data, laying out the ages that boys hit puberty in modern America, had previously been unavailable. "All parents need to know whether their sons are maturing within the contemporary age range, but, until now, this has not been known for US boys," said Richard Wasserman, director of the AAP's practice-based research network. The study, to be printed in next month's edition of the journal "Pediatrics" was put online Saturday to coincide with an AAP conference in New Orleans."