As an RN I can tell you what causes earlier menses in women, it meat and its not because of hormones in it. It because women eat more of it now than they did, say, 100 years ago. Protein is what controls ALL blood flow, clotting etc. Take albumin, a protein in the blood, it controls how our cappilaries exchange O2 and CO2 through pressure. When women have higher concentrations of protein in their syestem, they naturaly tend to have menarche earlier. Just look at the differance in MAerican girls (average age of menses 12 yrs) as compared to that of under devoloped contries or even Asia where meat and protein consumption as a whole is decreased, they can average as high as 15!
The big question that people need to be looking at is this; teenage pregnancy rates have plummated in the last 20 years, but studies show that teens are still practicing unsafe, unprotected sex at about the same levels, and studies show that teen preganancy may be dropping due to higher levels of infertility in men. Why? Some studies show that its becasue of the same reason that women have menses earlier, others say that humans as a whole are becoming more monagomous and the sperm does not have to "compete" with other sperm, is this an argument for polygamy? I hope not.
As for birth control that elimanates menarche, Depo Provera does just that in about 80% of women who use it long term, however long term use (especially by young women) has shown to increase bone mineral density loss. Its a loss/loss no matter what you do.
Or how about this, insurance will not pay for birth control becasue it is "elective" but then will cover the delivery...wouldn't it be cheaper for them to just cover the damn pill so everyone else wouldn't have to payer higher premiums because of unwanted pregnancies?