From VOA Learning English, this is the Health & Lifestyle report.Much is unknown about the disease COVID-19.But health experts say they do know this: Age makes a big difference as to whether a person infected with the new coronavirus lives or dies.The reason is something called "reserve capacity."The Associated Press spoke with several doctors about the subject.One of them is Richard Baron, an expert in health care for older adults.He heads the American Board of Internal Medicine, a non-profit group.Baron notes that "at age 18, you have a lot of extra lung capacity you don't use unless you're running" a long race.He said that the ability of our lungs to process the air we breathe decreases with age, even in healthy people.So, the lungs of older men and women do not have this extra capacity."If you're an old person," said Baron, "even a mild form can overwhelm your lungs if you don't have enough reserve."The new coronavirus is like most respiratory viruses. It affects the movement of air into and out of the lungs.