Editor’s note: The podcast Chasing Life With Dr. Sanjay Gupta explores the medical science behind some of life’s mysteries big and small. You can listen to episodes here. (CNN) — Puberty: It’s one of ...

“Starting in 2010 … we knew that the average age of breast development for a girl fell somewhere between 8 and 9 in this country,” she said. “And for boys, the start of puberty looks like testicular ...