Brain clocks capture diversity and disparities in aging and dementia across geographically diverse populationsBrain clocks, which quantify discrepancies between brain age and chronological age, hold promise for understanding brain health and disease.However, the impact of diversity (including geographical, socioeconomic, sociodemographic, sex and neurodegeneration) on the brain-age gap is unknown.We analyzed datasets from 5,306 participants across 15 countries (7 Latin American and Caribbean countries (LAC) and 8 non-LAC countries).Based on higher-order interactions, we developed a brain-age gap deep learning architecture for functional magnetic resonance imaging (2,953) and electroencephalography (2,353).The datasets comprised healthy controls and individuals with mild cognitive impairment, Alzheimer disease and behavioral variant frontotemporal dementia.LAC models evidenced older brain ages (functional magnetic resonance imaging: mean directional error = 5.60, root mean square error (r.m.s.e.) = 11.91;electroencephalography: mean directional error = 5.34, r.m.s.e.= 9.82) associated with frontoposterior networks compared with non-LAC models.Structural socioeconomic inequality, pollution and health disparities were influential predictors of increased brain-age gaps, especially in LAC (R² = 0.37, F² = 0.59, r.m.s.e.= 6.9).An ascending brain-age gap from healthy controls to mild cognitive impairment to Alzheimer disease was found.In LAC, we observed larger brain-age gaps in females in control and Alzheimer disease groups compared with the respective males.The results were not explained by variations in signal quality, demographics or acquisition methods.These findings provide a quantitative framework capturing the diversity of accelerated brain aging.The brain undergoes dynamic functional changes with age 1-3 .Accurately mapping the trajectory of these changes and how they relate to chronological age is critical for understanding the aging process, multilevel disparities 4,5 and brain disorders 1 such as the Alzheimer's disease continuum, which includes mild cognitive impairment (MCI) and related disorders like behavioral variant frontotemporal dementia (bvFTD) 6 .Brain clocks or brain-age models have emerged as dimensional, transdiagnostic metrics that measure brain health influenced by a range of factors [7][8][9] , suggesting that they may be able to capture multimodal diversity 10 .Populations from LAC exhibit higher genetic diversity and distinct physical, social and internal exposomes 11,12 that impact brain phenotypes 4,13,14 .Income and socioeconomic inequality 15,16 , high levels of air pollution 17 , limited access to timely and effective healthcare 18 , rising prevalence of communicable and noncommunicable diseases 19,20 , and low education attainment 21,22 are determinants of brain health in LAC 18 .Thus, although measuring the brain-age gap could enhance our understanding of disease risk and its impact on accelerated aging 23 , there is a lack of research on brain-age models