Photometric studies on globular cluster systems in early-type galaxies are widely used to resolve stellar populations in these galaxies. The knowledge of the age and metalicity structure within the globular cluster systems allows to set constraints on the major star formation episodes in the galaxy. Here we present our method of detecting age sub-populations in globular cluster systems based on optical/near-infrared observations and Monte-Carlo simulations. It is based on the determination of the cumulative age distribution and its comparison to simulated globular cluster systems. On various galaxies we will demonstrate the ability of our method to detect age sub-populations and show how we use the derived age structure to find correlations between various galaxy parameters and the formation/evolution of a given galaxy.