In modern conditions of active aging of the population, it is especially important to study the age structure of the population. This article reflects regional characteristics of the age structure during the years of the census in the Republic of Belarus, in 1999, 2009, and 2019. The purpose of this study is to analyze the age structure of the population and the peculiarities of its transformation in the context of the regions of the Republic of Belarus by constructing sex and age pyramids. Age-sex pyramids made it possible to visually display the age-sex structure of the regional population in dynamics and identify the nature of its changes. Based on them, we can conclude that the population in five-year age intervals has decreased, and the most voluminous part of the pyramid has shifted upward, to older age intervals. The transformation of the age structure of the population towards an increase in the proportion of elderly people represents a certain set of tasks. Such a demographic shift can have an impact on the pension system, the health care system, and social protection authorities. The study of this issue made it possible to identify problems and opportunities associated with various age groups of the population, as well as to understand the socio-economic consequences of demographic aging of the population in Belarus. Information about the composition, dynamics, and problems related to the age structure can be used to develop and plan measures and strategies within the framework of demographic policy.