Elevated plasma levels of phosphorylated tau proteins (p-tau217, p-tau181), neurofilament light chain (NfL), and glial fibrillary acidic protein (GFAP) significantly reduced odds of achieving healthspan—survival to age 90 without cognitive impairment—in a cohort of 2,576 cognitively normal older women. The strongest predictor was p-tau217, which cut healthspan odds by 42%. This preprint awaiting peer review represents a paradigm shift in understanding these biomarkers beyond their established role in Alzheimer's diagnosis. The findings suggest these proteins reflect broader systemic aging processes rather than disease-specific pathology alone. For clinical practice, this could transform how we assess aging trajectories and identify individuals at risk for accelerated decline decades before symptoms appear. The research establishes a new framework for precision longevity medicine, though the study's limitation to older women and observational design means causality remains unclear. If validated through peer review, these biomarkers could become powerful tools for personalized aging interventions, moving beyond reactive dementia care toward proactive healthspan optimization.