Essentially, everyone has two ages: a chronological（按时间计算的）age, how old the calendar says you are, and a biological age, basically the age at which your body functions as it compares to average fitness or health levels.
"Chronological age isn't how old we really are. It's merely a number," said Professor David Sinclair at Harvard University. "It is biological age that determines our health and ultimately our lifespan. We all age biologically at different rates according to our genes, what we eat, how much we exercise, and what environment we live in. Biological age is the number of candles we really should be blowing out. In the future, with advances in our ability to control biological age, we may have even fewer candles on our birthday cake than the previous one."
To calculate biological age, Professor Levine at Yale University identified nine biomarker(生物标志) that seemed to be the most influential on lifespan by a simple blood test. The numbers of those markers, such as blood sugar and immune(免疫的) measures, can be put into the computer, and the algorithm（算式;算法）does the rest.
Perhaps what's most important here is that these measures can be changed. Doctors can take this information and help patients make changes to lifestyle, and hopefully take steps to improve their biological conditions. "I think the most exciting thing about this research is that these things aren't set in stone," Levine said. "People can be given the information earlier and take steps to improve their health before it's too late."
Levine even entered her own numbers into the algorithm. She was surprised by the results. "I always considered myself a very healthy person. I'm physically active; I eat what I consider a fairly healthy diet. But I did not find my results to be as good as I had hoped they would be. It was a wake-up call," she said.
Levine is working with a group to provide access to the algorithm online so that anyone can calculate their biological age, identify potential risks and take steps to improve their own health in the long run. "No one wants to live an extremely long life with a lot of chronic（慢性的）diseases," Levine said. "By delaying the development of mental and physical functioning problems, people can still be engaged in society in their senior years. That is the ideal we should be pursuing."
