This is one of those topics where your research numbers are going to be a little bit behind what doctors are actually seeing. That is, doctors see these girls and collect data, which is later interpreted by researchers, so they’re always a little behind the curveball.
As of 2003, the average age of menarche in the US was somewhere between 12 and 13, depending on what study you’re looking at and what population you’re looking at. This was only 3 months younger than reported in 1973. Fewer than 10% of girls in 2003 got their period before age 11. http://thesocietypages.org/socimages/2008/09/19/changing-biology-age-at-first-menstruation/ http://www.ncbi.nlm.nih.gov/pubmed/12509562
Now, and this came as a total shock to me, 2003 was almost 10 years ago! In those 10 years, we’ve seen a lot more fat kids, and girls with more body fat tend to get their periods sooner. We’ve also seen a rise in the percentage of non-white girls as a total of our population of girls, and they tend to get their first periods a little sooner than other girls. So it’s entirely possible that the average age has dropped a little more since 2003. But if it’s dropped by five years, I’d be exceedingly surprised. That’s how much menarche dropped between starving peasants in feudal Europe (17 years) and well-nourished 21st century. That’s an incredible lot. That falls into the “extraordinary claims” category - I’d ask that doctor what studies he’s basing his statement on. His claim, he’s got to support it.
That being said…yes, you do have to talk to her sooner than you think, if you were waiting until she’s 12 or starts bleeding to start The Talk. “The Talk” is rather passe, anyhow, and it’s generally recommended that you have many small Talks, beginning in early childhood, keeping an open dialogue of age-appropriate information. Most parents who plan one The Talk end up doing it far too late, after their kids have all sorts of nonsense in their heads (and sometimes babies in their bodies!) from their classmates. It’s actually much easier on you both to have many small talks than one long embarrassing lecture. If you need some tips on how to broach the topic(s), I quite like this guide: http://kidshealth.org/parent/positive/talk/questions_sex.html By 6, most kids are ready for sperm-and-egg-make-a-baby level of information, as well as, “boys and girls have different body parts and we don’t let anyone touch anything covered by a bathing suit unless it’s a doctor” and “we don’t have to keep bad touches a secret; that secret is okay to tell”.
One of my favorite books to introduce hard topics is called It’s Not the Stork! It covers not only sexual stuff, but bullying/how to be a good friend, the range of what families look like, etc. It’s a fantastic book to read with your kid and start those difficult conversations.