I imagine there is more than one factor involved here.

U.S. girls keep hitting puberty earlier

reuters.com

“The researchers said maturing at a younger age could come with long-term risks for some girls.

“For instance, those who hit puberty earlier could be at higher risk of breast and other cancers because their bodies spend more years making and being exposed to estrogen.

“They also tend to start having sex or using drugs and alcohol at younger ages and are more likely to become depressed or develop low self-esteem.”

Yes, I’ve seen adolescent girls around here who, from a distance, you would think were overweight middle-aged women, suffering from a slowed-down metabolism. These kids are eating too much (esp junk food), are not getting exercise, and with earlier development are becoming sexualized at a much younger age, even before middle school. But it’s not their fault. They are children, after all. Our job as adults should be to protect and educate our kids, not exploit them, as they transition into adulthood. When I see a young girl with her mother and they’re dressed in the same outfits, it’s depressing. They are not peers—they’re parent and child, but our obsession with youth also tends to drive what we wear and how we look as adults, as well.

“You’ve got a 10-year-old who looks like a 14-year-old. We interact with kids based on the way that they look,” Biro said. “Kids interact with each other that way also.”