Puberty is triggered by a complex set of hormones and is one of the major physical milestones that occur during adolescence. Menarche, a girls first menstrual period, typically occurs between the ages of 11 and 15. This age is a drastic change from the mid-19th and mid-20th centuries when the average age of menarche was 17!
There have been many suggestions as to why this has changed; one is the change in diet and lifestyle - mainly increases in protein and fat intake.
Why do you suppose the increase in fat and protein affect the timing of puberty?