["Review of Development Economics, EarlyView. ", "\nABSTRACT\nDiminishing fertility rates and an aging population hinder households' energy savings through economies of scale. In contrast to prior annual analyses, we combine the daily electricity consumption records with household survey data for rural households in a northern Chinese province from 2016 to 2018 to quantify age‐specific scale effects on electricity consumption. Our analysis indicates that a reduction of one child increases per capita usage by 15.7%, while a reduction of one older adult increases it by 9.0%, demonstrating that fewer children and more seniors reduce scale advantages. Economies of scale are more pronounced for low‐income, less educated families with young children and female members, highlighting inequalities associated with these variables. We additionally demonstrate that temperature changes and holidays exacerbate age‐related energy disparities. Moreover, considering the demographic shifts, we anticipate a 6.4% increase in per capita household electricity consumption by 2030. Our findings offer detailed, daily evidence to inform age‐sensitive, demand‐side policies that improve energy efficiency, equity, and climate adaptation, thus promoting sustainable development.\n"]