The ‘Theory of Visual Attention’ quantifies an individual’s capacity of attentional resources in parameters visual processing speed C and vSTM storage capacity K. By combining TVA-based assessment with neurophysiology, we showed that distinct ERP components index inter-individual differences in these two functions: The posterior N1 was smaller for participants with faster relative to slower processing speed and the Contralateral Delay Activity (CDA) was larger for participants with higher relative to lower storage capacity. When we extended the approach to investigate neural underpinnings of age-related changes in attentional capacities, these ERP markers of individual differences in processing speed and storage capacity were validated in an older group. Furthermore, additional components were related to performance exclusively in older inidividuals: Anterior N1 amplitudes were reduced for slower older participants (relative to younger and faster older participants) and high-storage capacity older participants (relative to younger and low-storage capacity older participants) obtained a stronger right-central positivity, which correlated with K-values only in the older group. Our findings indicate that reorganization of attentional brain networks, including age-specific decline and compensation mechanisms, determines older individuals’ attention capacity. Furthermore, we show that the distinctiveness of the two functions, as defined in TVA, is preserved (or even increased) in older age.