We all know someone who radiates timeless youth. Their energy is contagious. Their skin glows. And their vibrancy is unmatched. Conversely, others seem to age before their time. Are these variations purely by chance? Or luck? Not quite. In fact, your biological age—the true measure of how well you’re aging—might not match the number of candles on your birthday cake. Knowing your biological age is remarkably empowering. It keen insights into how your lifestyle and genetics affect your well-being. Scroll for the 411 on biological age, how to measure it, and actionable ways to turn back the clock.

Featured image from our interview with Megan Roup by Michelle Nash.