How old are you, really? Your chronological age is the number of years you have been alive. Your biological age is how old your cells are which scientists believe may better assess one’s age-related health and disease risk. People biologically age at different rates, depending on genetic and environmental factors, so that a person’s chronological age does not necessarily match their biological age. In recent years, direct-to-consumer biological age tests have become increasingly accessible and popular as interest has increased in this nascent science.