Children are starting puberty earlier than in the past, potentially due to a combination of environmental, lifestyle, and metabolic factors – but the reasons why are still puzzling scientists. On average, girls start puberty at age 11, while boys start at 12. But if girls enter puberty at age 7 or younger, or if boys start at age 8 or younger, they may be diagnosed with precocious puberty, which can lead to long-term health problems like obesity, diabetes, mental health issues, and breast cancer. When doctors first identified the shift toward earlier puberty among American girls in the 1990s, …