Metacontrol, the ability to adapt cognitive control to task demands, declines with age and is thought to be reflected in aperiodic and periodic neural dynamics. Given that anodal transcranial direct current stimulation (atDCS) can modulate cortical excitability via membrane potential shifts, we tested whether atDCS alters the neurophysiological signatures of metacontrol in younger and older adults. In a mixed design, younger and older participants performed a Go/Nogo task under both atDCS and sham stimulation conditions; resting-state EEG data were also acquired. Aperiodic activity was analyzed using the FOOOF algorithm, and periodic activity was examined through time–frequency analysis. Behaviorally, younger adults showed higher accuracy and faster responses than older adults, but no significant stimulation effects emerged in either group. Results showed that, compared to sham, aperiodic activity (FOOOF exponent) increased after atDCS, particularly in older adults, indicating a steepening of the EEG spectrum and thus increased inhibitory tone in the aging process. However, resting-state aperiodic activity did not predict stimulation-induced effects within either group. In the periodic domain, we found no evidence that atDCS modulated task-related theta or alpha power. Moreover, exploratory analyses revealed no significant associations between atDCS-induced changes in the aperiodic exponent and oscillatory power. This dissociation indicates that, under the present conditions, the periodic and aperiodic components of the EEG signal reflect distinct and likely independent neurophysiological responses to neuromodulation. Targeting metacontrol mechanisms through neuromodulation may, with further validation, open new avenues for supporting cognitive health in older adults.