What concept do scientists use to estimate the body's true wear from cells and molecules?

Biological age is the concept scientists use to estimate how worn or aged a body's cells and molecules actually are, often measured through markers like DNA-methylation patterns that can diverge meaningfully from a person's simple calendar age, capturing wear and tear that a birthday count alone can't reveal.

Resting heart rate is a useful general fitness indicator but reflects cardiovascular conditioning specifically, not a comprehensive estimate of cellular aging across the whole body. Body mass index is a rough ratio of weight to height used to categorize body size, also not a direct measure of biological wear.

Longevity researchers hope that lowering someone's biological age relative to their calendar age could translate into a longer, healthier life, but treatments aimed at doing this remain experimental, and reliably measuring biological age itself is still an active area of scientific debate.