Groundwater age is an important water property used as an indicator of groundwater quality. There have been no sufficient data and measurements underground, and that problem has been mitigated by using direct simulation of groundwater age. This paper has been motivated by the work of Daniel J. Goode, defining a rather different approach. A numerical model has been developed, using the Lagrangian approach and random walk particle tracking method, where groundwater age is calculated as a summed-up travelling time of certain particles. Basic input of this method is flow calculation; hence, in order to get the groundwater age simulation, an upgrade has been done to the existing software. Synthetic examples have been simulated for homogeneous, layered, as well as for low and medium heterogeneous aquifer systems. A stochastic analysis of heterogeneous aquifers has been done using a Monte Carlo simulation method. The results are given as groundwater age fields. Application of such an approach lays in possible estimation of the expected groundwater age at a certain location of water intake. Therefore, the calculated probability assumptions may be used as a decision support tool in cases of groundwater pollution, estimation of the level of aquifer's auto-purification, or in events where applying certain level of water treatment prior to usage is needed.