Slowing Down with Age? Senescence slows everyone down, but most adults have unused reserves. Consider Lizzy Hawker, about 100 pounds and 5 feet, 4 inches tall, who entered her first race at age 28 and has been running longer and faster every year since. Here she is a mile and a half above sea level (2,632 meters) in the Swiss Alpine Marathon, which she won in 2007. Five years later, at age 37, she ran 100 miles around Mount Blanc, again winning.