Aging Unequally: Functional Age Disparities Between Developmental and Non-Developmental Disabilities

<b>Background</b>: Adults with developmental disabilities often experience accelerated aging, but the magnitude of this phenomenon is not well quantified. This study aimed to measure the disparity in functional ability and chronic illness prevalence between adults with developmental and other disabilities. <b>Methods</b>: A "functional age" was calculated for adults with developmental disabilities. This metric, designed as a statistical index of disparity, was derived from normative regression models of ADL and IADL based on a reference group of adults with other disabilities. <b>Results</b>: A profound gap was found between chronological and functional age. On average, a 44-year-old individual with a developmental disability exhibited a level of functional limitation equivalent to a person over 100 years older in the reference population for both ADL and IADL (<i>p</i> < 0.001). <b>Conclusions</b>: Accelerated aging in this population manifests as a severe, early onset functional disadvantage rather than an elevated burden of general chronic disease. Policies should shift toward function-based, not age-based, models of care to address these lifelong support needs.