Girls are now reaching puberty before age 10

And that's an average age of puberty - not an outlying limit for precocious individuals:

Scientists have found that the average age that breast development begins is now nine years and 10 months – almost a year earlier than a previous study in 1991.

They have yet to discover the reason behind the phenomenon but believe it could be linked to unhealthy lifestyles or exposure to chemicals in food.

The study was carried out in Denmark in 2006, the latest year for which figures were available, but experts believe the trend applies to Britain.

Data from America also points to the earlier onset of puberty.

In the nineteenth century the average age of onset of puberty in females was 15.  By the 1960s it was about 12.  Now it's under 10.

Lots of implications, some of them discussed a different article in The Telegraph:

These girls are towering over boys of their own age because, for girls, the growth spurt and development of breasts come first; periods come later. With boys, it is the other way round: their genitalia and sweaty armpits develop before their height shoots up. The last stage of the maturing process, when they are finally able to signal their manliness, comes when their voices break.

All these markers have been occurring steadily earlier for both boys and girls, but recent changes have been dramatic. In the 18th century, when Bach was directing the Leipzig choir, the average age at which a boy’s voice broke was 18. Choirmasters now have trouble finding trebles over the age of 13 or 14...

Parents, too, should be careful not to treat them as teenagers. “They need to look at their emotional, not their physical, development.

Photo credit PA.