As any doting parent can tell you, kids sure do grow up quickly. But now, they actually are growing up faster than ever.

For girls, this news is nothing new. Pediatricians and researchers documented 15 years ago that girls were entering puberty earlier than they used to. But only recently did the American Academy of Pediatrics demonstrate that boys are also beginning to mature as much as two years earlier than previously recorded.

The study showed that African-American boys show signs of puberty at age 9, on average, while the average white or Hispanic boy enters this stage of maturity at age 10. Genes influence when puberty begins, which accounts for the differences among races.

The study, led by the American Academy of Pediatrics, was exhaustive. Two hundred pediatricians in 41 states recorded information on 4,131 boys between the ages of 6 and 16.

Scientists have used their understanding of girls’ earlier maturation to study its connections to everything from obesity in children to infertility issues women might encounter later in life. Heavier girls are generally believed to enter puberty earlier — a fact that shouldn’t come as a surprise, given that body fat is connected to the body’s production of estrogen.

The study gives parents better information about normal expectations for their sons. But researchers stress that just because they now know that boys mature faster doesn’t mean they are any closer to understanding why.

Theories abound. Could higher obesity levels and more video games be at fault? Perhaps the chemicals in processed food are to blame? Researchers simply don’t know.

As for parents, this new knowledge might not help them much. They are seldom equipped for the changes puberty brings, no matter when it starts.