Community-based care services offered by senior centers are vital for supporting older adults’ independent living. The number of senior centers has escalated in China in recent years. Despite scholarly interest in the potential accessibility of senior centers, research on older adults’ realized access remains scarce. Using the geo-referenced check-in data of 2382 users of senior centers in Nanjing, China, this study aims to fill this gap by examining the disparities between older adults’ potential and realized access to senior centers and the influence of multilevel spatial and non-spatial factors. This study indicates that potential access is often significantly overestimated compared with the actual accessibility of senior centers, with older adults’ distances of realized access (mean = 1319 m) being considerably greater than potential access (mean = 325 m). Spatial and regression analyses confirm that older adults living in newly built, lower-priced houses in the inner city are more likely to travel longer distances to reach senior centers. Spatial proximity is less effective in predicting realized access for those living further from senior centers. Instead, the location and service quality of senior centers play a more prominent role. These findings enrich our understanding of older adults’ access to community-based care, informing planning and policy interventions for the development of age-friendly communities.