The article is focused on the problem of the existing imbalance in the age structure of S&T personnel in Russia, expressed in the strong dominance of the group of young researchers. Highlighting examples demonstrated the influence of the government on the occurrence of such an imbalance. The literature review contains analysis of approaches to measure the most productive scientists' age in different fields of knowledge and to construct research labs' age structure models. The optimal S&T personnel age structure in Russia is estimated using the model «predator-victim». It is shown that the role of three age groups: young, mature and elderly researchers - in different countries (Russia, France and the UK) is different. To build the model, the hypothesis is formulated that only two age groups are active, and the third plays the role of balancing the staffing segment. Experimental calculations have confirmed this hypothesis. Two scenarios of its formation - demographic (natural inflow and outflow of personnel) and competitive (model reproduction of researchers' interaction) are considered to identify the degree of intensity of the S&T personnel age structure, which set the interval of acceptable values for the actual shares of age groups. It is shown that the problem of shortage of mature researchers is not a typical Russian problem, but to a large extent is typical for developed European countries; the specificity of the Russian model of scientific personnel reproduction, in which all the problems are aggravated, is considered. The issues of choosing an adequate policy to reduce the negative trend in the formation of the age structure of Russian researchers are discussed.