The age of a human being is a common research topic in many branches. This topic is also addressed by the legal theory. Age categories also functioned in Roman law, determining the legal position of a person. In this article, the non-judicial sources which concerned the division of human life are analyzed. Consequently, it has been possible to determine that in ancient Rome, there were several theories concerning this matter. The division of life into three, four, five, six or seven stages was very popular. Each theory has different justifications and various arguments. Among those, we can distinguish medical, psychological, numerical and also military-administrative arguments.