Stiff muscles after a day spent in nature can make a person feel old, but nature can also make us feel young. Compared to a butterfly, our lifespan is enormous. Compared to the stars, we are less than infants. The sense of discovery, excitement of learning new things, delight in following our curiosity, and freedom from the constraints of polite society all contribute to our feelings of joy and vibrancy and youthfulness in nature—no matter what our true age.