Individual differences in human brain aging are difficult to estimate over short intervals because of measurement error. Using a cluster scanning approach that reduces error by densely repeating rapid structural scans, we measured brain aging in individuals in one year. Expected differences between young and older individuals were evident, as were differences between cognitively unimpaired and impaired individuals. Each person's brain change trajectory was compared to modeled expectations from a large cohort of age-matched UK Biobank participants. Cognitively unimpaired older individuals variably revealed relative brain maintenance, unexpectedly rapid change, and asymmetrical change. These atypical brain aging trajectories were found across structures and verified in independent within-individual test and retest data. Precision estimates of brain change are possible over short intervals and reveal marked variability including among cognitively unimpaired individuals.