Chronological vs biological age
Chronological age — the time since your birth — is the number every age calculator returns. Biological age estimates how old your body 'acts' based on physical and biochemical markers: VO2 max, resting heart rate, blood pressure, grip strength, body composition, telomere length, and DNA methylation. Two 50-year-olds can have biological ages 10-15 years apart depending on exercise, diet, sleep and chronic stress. Researchers use biological age in longevity studies; doctors use it to calibrate health risk. Chronological age is universal and simple; biological age requires testing but better predicts disease risk and life expectancy. Calculators handle chronological — biological needs a lab.