How Old Are You, Really? New Tests Want to Tell You

Age is just a number—and one you may be able to change. At least that’s the pitch behind Tally Health, a new startup that’s among a crop of companies selling tests that offer to tell consumers their “biological age.”

You’ve heard of at-home tests like those from 23andMe and Ancestry, which scan your DNA to provide information about ethnic heritage and health risks. Now, a wave of startups is marketing tests that claim to parse your blood, urine, or a cheek swab to reveal your biological age. The tests measure epigenetic patterns, or changes in the body that affect how genes behave. Unlike a calendar age, which marches along at the same pace for everyone, biological age is the speed at which cells, tissues, and organs appear to decline—and that can vary, depending on a person’s health history.

Tally Health, which launched last week, is one of around a dozen companies that offer these tests. Harvard University biologist David Sinclair, the company’s cofounder, describes its version as something like a credit score for your body. You swab your cheek and drop your…