Age is the primary risk factor for Parkinson's disease (PD), but how aging changes the expression and regulatory landscape of the brain remains unclear. Here, we present a single-nuclei multiomic study profiling shared gene expression and chromatin accessibility of young, aged and PD post-mortem midbrain samples. Combined multiomic analysis of midbrain nuclei along a pseudopathogenesis trajectory reveals all glial cell types are affected by age, but microglia and oligodendrocytes are further altered in PD. We present evidence for a novel age-associated oligodendrocyte subtype that appears during normal aging, characterized by elevated protein folding and chaperone-mediated autophagy pathways. Differential gene and protein-protein interaction analyses show that these functions are significantly compromised in PD. Peak-gene association from our paired data identifies differential cis-elements linked to regulation of differentially expressed genes between PD patients and neurologically healthy controls. Our study suggests a previously undescribed role for oligodendrocytes in aging and PD pathogenesis.