[Damorian]

Related, girls (women?) are starting their periods about 5 years sooner compared to 100 years ago: https://en.wikipedia.org/wiki/Menarche#Changes_in_time_of_av...

[perardi]

Per Wikipedia, and other sources I’ve read, it seems heavily correlated with BMI.

Which…makes a naïve sort of evolutionary sense. You need some percentage of body fat for your body to kick into reproduction mode.

[joncrane]

This has to do more with better nutrition and comfort than anything else.

While it's true that estrogen-like compounds may also have an effect, it takes calories to ovulate and to menstruate.