Rapid online control (ROC) enables in-flight movement adjustments when targets shift unexpectedly and is critical for everyday function and safety, particularly in aging. Laboratory studies have reported mixed findings on age-related changes in ROC, with some attributing differences to general motor slowing. A recent lab-based study (Wang et al., 2025) demonstrated that older adults' prolonged correction latencies could not be fully explained by slowing and were linked to motor imagery ability. The present study replicated and extended these findings in a larger, continuous adult lifespan sample (N = 241; ages 20-79) using an online double-step reaching paradigm with mouse-cursor tracking. Linear mixed-effects models revealed robust age-related declines in ROC, characterized by longer correction latencies and more rigid corrective movements, even after accounting for device variability and general slowing. Participants increasingly relied on a speed-accuracy trade-off strategy with age, extending movement durations to preserve endpoint accuracy. While older adults' correction latency was linked to their motor imagery efficiency, unlike the previous lab study, the endpoint accuracy was not associated with motor imagery but primarily dependent on the kinematic feature of correction deviation. Moreover, response inhibition, measured by the stop-signal task, emerged as a robust predictor of correction efficiency across the lifespan. These findings confirm age-related declines in ROC under more heterogeneous, real-world conditions and show mouse-cursor tracking as a viable method for large-scale, online studies of motor control across the adult lifespan. (PsycInfo Database Record (c) 2026 APA, all rights reserved).