Analysis of 18,571 adults aged 50 and older across five longitudinal aging cohorts reveals that prediabetes significantly accelerates frailty progression and functional decline over a median 13.6-year follow-up. Prediabetes (HbA1c 5.7-6.4%) increased deficits in activities of daily living and instrumental activities of daily living, while accelerating progression on the Frailty Index compared to normoglycemia. Among those with baseline prediabetes, 20.8% regressed to normal glucose levels while 24.3% progressed to diabetes. The findings challenge assumptions about prediabetes as merely a "warning stage" before diabetes. Instead, prediabetes appears to represent an active pathophysiological state driving age-related decline through mechanisms potentially involving chronic inflammation, insulin resistance, and metabolic dysfunction. The scale of this analysis—spanning multiple countries and cultures—strengthens confidence in these associations. However, this preprint awaits peer review, and the observational design cannot establish causation. The counterintuitive finding that regression to normoglycemia was associated with increased deficits warrants scrutiny and may reflect residual confounding or measurement timing issues that peer review should address.