I have a VERY hard time believing that to be true. While early onset of puberty may trigger earlier sexual activity, I see no way the opposite can happen.
I say that as the mother of an 11 year old daughter who has physically developed far earlier than I did. I have girls ranging in age from 6-14 in and out of my house on a regular basis, and some of those girls have bodies that many 18 years olds would die for. Heck, I'm 49 and I never had a body like some of them have. SIGH :(
The sad thing is, they are still little girls, but because of how they look they are not taken for what they really are.
They still love to play dress up, and my stash of cocktail dresses and evening gowns are among their favorites (another mom, with a similar collection is another fave.) It's fun for them because they are still little girls and want to play princess. They also know that they can have their fashion shows and put on makeup, but they do it in the house and all makeup is removed before they get ready to leave or even go outside to play.
I don't know why these girls are developing so early, but it is up to the parents to teach them what they need to know, but also to remember that regardless of what they look like, they are still children and need to be treated and protected as such.
Studies have shown (I know, those words ...) that exposure to sexually-explicit media and sexual behavior is *one* factor in *some* instances of earlier onset of puberty. There's also a correlation with the residence of non-family-member males in the household (e.g., Mom's latest sex partner). There was some discussion of a hormonal mechanism; that is, actual causation rather than simply correlation.
The book that detailed all this, with footnotes, is called "Early Puberty," iirc, and it also observed that *weight* is the major factor in the lower average age of puberty.
The latest theory I have read to explain the earlier onset of puberty are;
Better nutrition and less exercise.
A higher percentage of body fat in young girls leads to an earlier onset of puberty. Less exercise by today’s girls leads to the girls carrying extra body fat. Estrogen is fat soluble which means that the girl bodies retain more estrogen than they would if they carried less fat.
Athletic girls (such as swimmers and gymnast) tend to enter puberty later. This is attributed to their lower body fat.
“my stash of cocktail dresses and evening gowns”
I knew that was you!