The age at which girls are reaching puberty is steadily falling. In 1840, the average girl was 16.5 years when she attained menarche—the onset of menstruation. By 1920, the age had dropped to 14.6; by 1950, it was 13.1; in 1980, 12.5; and 12.43 in 2020. By 2022, the percentage of U.S. girls who reached…