Introduction Cognitive aging increases vulnerability to false memories, yet the neural mechanisms underlying age-related susceptibility across sensory modalities remain poorly understood. Most previous studies have focused on visual orthographic stimuli, leaving the neural dynamics of auditory false memories largely unexplored. Methods To examine whether age-related susceptibility to semantic illusions is modality-specific and to characterize its spatiotemporal neural dynamics, we employed a cross-modal Deese–Roediger–McDermott (DRM) paradigm including Visual and Auditory conditions. Sixty-four-channel electroencephalography (EEG) was recorded from healthy younger and older adults. Event-related potentials (ERPs) were analyzed over frontal (300–500 ms) and parietal (600–800 ms) regions to assess familiarity-related and post-retrieval monitoring processes. Results Behaviorally, older adults maintained robust old-lure discrimination accuracy in the Visual condition but showed reduced performance in the Auditory condition, characterized by increased false alarms and prolonged reaction times for correct rejections. Electrophysiologically, visual lures elicited a classic FN400 familiarity effect together with relatively preserved late parietal monitoring responses across both age groups. In contrast, auditory lures elicited an early N400-like effect suggestive of increased semantic conflict processing. While younger adults appeared to recruit late parietal monitoring resources to resolve this auditory conflict, older adults showed attenuated and less organized late parietal monitoring activity. Discussion These findings provide preliminary evidence for a modality-dependent vulnerability to false memories in cognitive aging. The results suggest that auditory false memories may arise from increased semantic conflict combined with reduced late-stage monitoring processes, highlighting a potential modality-specific mechanism underlying age-related memory distortions. Pending further replication, these findings may contribute to a better understanding of false-memory vulnerability in older adults.