What is biological age?

Biological age attempts to estimate the true condition of your body, independent of your chronological age. It reflects the “wear,” “efficiency,” and “functionality” of your tissues, organs, and metabolic processes.

Two people who are both 40 years old chronologically can differ biologically by a decade or more. One may have the metabolism and physical function of a 30-year-old, the other of someone in their fifties.

Biological age tries to answer the question:
“How old is your body, really?”

Although the concept is attractive, science agrees on one thing: there is no single measurement that fully captures how the entire organism is aging.

The reasons:

• aging is multidimensional,
• different systems age at different speeds,
• some tissues may be “younger” than others,
• different tests measure different layers of biology.

Examples:

• muscles may show low biological age,
• but your cardiovascular system may appear older,
• while the microbiome tells another story.

Therefore, talking about “one number” is always an oversimplification.

In short: biological age is intriguing and promising, but still imprecise and evolving.

Three main conclusions:

1. Yes — biomarkers exist that correlate well with aging.
   DNA methylation, inflammation markers, mitochondrial function, muscle strength.
2. No — no single test gives the full picture.
   Epigenetic clocks are impressive but cannot describe metabolic health, fitness, or strength.
3. Yes — some clocks predict disease risk and mortality very well.
   DunedinPACE predicts the rate of aging.

It’s a powerful tool — but still supplemental, not definitive.

Different experts have different views:

Peter Attia

• cautious about biological age as a concept,
• sees epigenetic clocks as promising but not yet reliable enough,
• prioritizes functional metrics: VO₂max, strength, DXA, BMD.

David Sinclair

• a pioneer of epigenetic research,
• much more enthusiastic about aging clocks,
• considers biological age a central metric,
• surrounded by controversy, which also affects interpretations of his work.

Bryan Johnson

• tracks biological age using many methods,
• openly shows that different tests give different results.

Andrew Huberman

• pragmatic approach,
• sees lifestyle and habits as the main anti-aging tools, clocks as secondary.

Biological clocks are tools that mathematically and molecularly estimate biological age based on observable changes in your biology.

They often use:

• DNA methylation,
• gene expression,
• protein composition (proteomic clocks),
• metabolites (metabolomic clocks),
• inflammatory markers,
• organ function metrics (VO₂max, DXA, grip strength).

Most well-known clocks:

• Horvath Clock
• Hannum Clock
• GrimAge
• PhenoAge
• DunedinPACE — measures rate of aging, not age.

They are powerful but still under active refinement, calibration, and validation.

They are related, but not the same:

Biological age

A result — an interpretive estimate of your body’s physiological state.

Biological clocks

Tools and algorithms attempting to calculate that estimate from biological data.

In short:

Biological age is the idea.
Biological clocks are the measurement systems.

• biological age = conceptual interpretation,
• clocks = specific tests generating estimates.

1. Different tests give different results

• 32 years epigenetically in Test A,
• 38 years in Test B.

2. Poor short-term repeatability

Results may shift between February and March.

3. Tests measure different biological layers

DNA methylation ≠ inflammation ≠ VO₂max ≠ muscle strength.

4. Risk of obsession and longevity overkill

The goal is not chasing numbers, but building real health.

The most meaningful predictors of longevity are objective functional metrics:

• muscle strength,
• muscle mass and body composition (VAT, BF%),
• VO₂max and endurance,
• metabolic health (glucose, insulin, ApoB),
• bone density (BMD),
• sleep quality,
• emotional resilience and stress regulation.

These determine:

• whether you climb stairs without breathlessness,
• whether you can pick up your grandchild,
• whether you avoid injuries,
• whether you stay mobile into your 70s–90s.

This is your true biological age.

Biological age is a fascinating lens — but still just a tool. It:

• helps, but does not decide,
• shows trends, not details,
• is evolving, not definitive.

What truly shapes your longevity:

• strong muscles,
• a healthy heart,
• a well-functioning metabolism,
• solid bones,
• restorative sleep,
• emotional stability.