Analysis of 2,384 older U.S. adults reveals diabetes accelerates biological aging by 0.76 standard deviations using the PhenoAge algorithm, while stroke produces the largest cognitive decline (β = -0.317). Accelerated biological aging mediated 88.5% of diabetes-related cognitive decline and 13.7-27.2% for other cardiovascular conditions like hypertension and heart disease. The study establishes biological aging as the primary pathway connecting cardiometabolic dysfunction to cognitive deterioration. This finding illuminates why interventions targeting biological aging markers might prove more effective than treating individual cardiovascular conditions in isolation for preserving cognitive function. The research advances our understanding beyond traditional chronological age measures, suggesting blood-based biomarkers could identify high-risk individuals before overt cognitive symptoms appear. However, mediation effects varied significantly across racial groups and sex, with stronger patterns among Non-Hispanic Whites and females, highlighting the need for personalized approaches. As a preprint awaiting peer review, these mediation percentages require validation, but the mechanistic pathway from cardiovascular risk through accelerated aging to cognitive decline represents a paradigm shift toward targeting biological aging processes rather than isolated disease states.