BACKGROUND AND AIMS: Reproductive history, including age at first childbirth, may be associated with female dementia prevalence and sex disparities. This study investigates the relationship between reproductive timing and dementia outcomes, emphasizing socioeconomic and cultural influences, particularly in low- and middle-income countries (LMICs) where disparities in healthcare and education may exacerbate risks. METHODS: Country-level ecological analysis was conducted using data from 204 countries. Variables were sourced from international databases, including the Institute for Health Metrics and Evaluation (IHME), the United Nations, and the World Bank. The primary outcomes were female dementia prevalence and sex disparity in dementia prevalence. Predictor variables included age at first childbirth, ageing in females, economic affluence, genetic predisposition, and urban living. Statistical methods included scatterplots, correlation analyses, partial correlations, stepwise multiple regression, and principal component analysis. RESULTS: Later age at first childbirth was strongly associated with increased female dementia prevalence (² = 0.7314,  = 126) and greater sex disparity in dementia outcomes (² = 0.6362, = 126). Subgroup analyses revealed stronger associations in LMICs than in high-income countries. Economic affluence was positively associated with both later age at first childbirth and higher female dementia prevalence. Other variables, such as ageing and genetic predisposition, also showed independent associations. CONCLUSION: Delayed age at first childbirth is significantly associated with higher female dementia prevalence and sex disparities, particularly in LMICs. These findings highlight the need for individual-level, longitudinal studies to explore potential causal pathways and to inform sex-sensitive public health strategies for dementia prevention across diverse global contexts.