The concept of brain maintenance refers to the preservation of brain integrity in older age, while cognitive reserve refers to the capacity to maintain cognition in the presence of neurodegeneration or aging-related brain changes. While both mechanisms are thought to contribute to individual differences in cognitive function among older adults, there is currently no ‘gold standard’ for measuring these constructs. Using machine-learning, we estimated brain and cognitive maintenance based on deviations from normative aging patterns in the Whitehall II MRI sub-study cohort, and tested the degree of correspondence between these constructs, as well as their associations with premorbid IQ, education, and lifestyle trajectories. In line with established literature highlighting IQ as a proxy for cognitive reserve, higher premorbid IQ was linked to cognitive maintenance independent of the degree of brain maintenance. No strong evidence was found for associations between lifestyle trajectories and brain or cognitive maintenance. In conclusion, we present a novel method to characterize brain and cognitive maintenance in aging, which may be useful for future studies seeking to identify factors that contribute to brain preservation and cognitive reserve mechanisms in older age.