Optimal design problems arising in mechanics of growing composite viscoelastic and elastic solids subjected to aging are considered. The growth means a continuous mass influx to the body surface. Due to this process, the size of the body increases in time. The mass influx with pretensioning causes the rise of stresses in the growing body. The purpose of the current study is to propose a new class of the optimal design problems for the growing viscoelastic composite solids subjected to aging, and to solve the mechanical design problems of this new type. In the current paper we analyze the optimal design of the shape of growing reinforced beams which minimizes their maximum deflection. The proposed approach and the obtained new solutions are of a special interest and importance for the design of the reinforced cantilevers and bridges.