Hypothesis: Individuals with lower pain tolerance (shorter withdrawal time in a standardized cold pressor test) exhibit accelerated epigenetic aging, as measured by GrimAge, independent of chronological age, physical fitness, and baseline inflammatory markers. This relationship is driven by mitochondrial dysfunction in primary sensory neurons that alters NAD+-dependent sirtuin activity, leading to dysregulated DNA methylation patterns at aging-associated CpG sites. We propose a three‑step mechanistic chain: (1) reduced pain tolerance reflects heightened neuronal excitability due to leaky mitochondrial ROS production in dorsal root ganglia; (2) chronic ROS efflux depletes local NAD+ pools, suppressing SIRT1 and SIRT3 deacetylase activity; (3) diminished sirtuin signaling fails to maintain repressive chromatin states at promoters of inflammasome and senescence genes, causing epigenetic age acceleration detectable in blood DNA. Prediction: In a cohort of 500 pain‑free adults aged 30‑70, baseline cold pressor tolerance will inversely correlate with GrimAge acceleration (β ≈ -0.30, p < 0.001) after adjusting for VO2 max, BMI, smoking, and IL‑6 levels. Furthermore, individuals in the lowest quartile of tolerance will show a 1.5‑fold higher risk of developing clinically significant age‑related decline (e.g., gait speed <0.8 m/s or MoCA drop ≥2 points) over a 5‑year follow‑up compared to the highest quartile. Falsification: If pain tolerance shows no association with GrimAge after controlling for fitness and inflammation, or if the direction is positive (higher tolerance predicts faster epigenetic aging), the hypothesis is refuted.