Be honest: Have you ever looked up someone from your childhood on social media with the sole intention of seeing how they've aged? One of my colleagues, who shall remain nameless, certainly has. He recently shared a photo of a former classmate. Can you believe we're the same age?" he asked, with a hint of...

This is today's edition ofThe Download,our weekday newsletter that provides a daily dose of what's going on in the world of technology. How aging clocks can help us understand why we age-and if we can reverse it Wrinkles and gray hairs aside, it can be difficult to know how well-or poorly-someone's body is truly aging....