However, with aging measurements we are able to determine an improvement or decrement to your health from exam to exam, from year to year. Within that range, a normal test result may or may not be normal for a specific person. We've found that you really have to consider each individual a case study of one. Rather than compare yourself with the entire population, it's better to compare your own results from exam to exam. So you're really comparing yourself to yourself.
Articles come out periodically about the inaccuracies and mistakes of medical tests.
It's a real problem. For example, blood pressure, which is included in many age-measurement test batteries, is notoriously variable. Just walking into an unfamiliar doctor's office can cause a person's blood pressure to increase significantly. This is a real problem with the current state of the art of aging measurement. However, as our understanding of aging increases and we find better biomarkers of aging, the measurement of biological age will become more accurate.