Adults aged 75 who developed cancer during a three-year study showed measurably accelerated biological aging—between 3.52 and 6.77 months faster than their chronological age—as measured by multiple epigenetic clocks including Horvath, Hannum, and PhenoAge. They also experienced greater functional decline, losing grip strength by 1.77 kPa and taking 0.64 seconds longer on sit-to-stand tests compared to cancer-free peers. This comprehensive analysis of 2,152 generally healthy older adults provides compelling evidence for the geroscience hypothesis—that cancer and aging share fundamental biological pathways. The finding that biological aging acceleration preceded noticeable functional decline suggests epigenetic clocks may serve as early warning systems for cancer vulnerability. While the study's strength lies in its large, healthy cohort and multiple aging biomarkers, the observational design cannot establish whether accelerated aging predisposes to cancer or cancer accelerates aging. For aging adults, this research underscores how cancer represents more than localized disease—it's a systemic accelerator of the aging process itself, potentially explaining why older cancer patients often experience broader health deterioration beyond their primary diagnosis.