The formation, shaping and evolution of galaxies are processes of high interest but poorly known. This is true also for our closest galactic neighbours. Of key importance is a representative sample of all major types of galaxies with solid evolutionary parameters. Stellar clusters are excellent probes of galactic evolution, albeit so far useful at smaller distances only, mainly due to the limiting effects of image crowding. With Extremely Large Telescopes (ELTs) with full adaptive optics (AO) and near diffraction limited performance, the effects of image crowding will be drastically reduced. Thus, the excellence of clusters of stars as evolutionary probes can be extended out to cosmological distances. We have studied this extension. With data on the Strömgren uvby system, based on direct measurements taken from the literature, we synthesised an open test cluster as well as a galactic background field. The cluster was embedded in the background and located at distances between one and 500 Mpc. y and b data were measured with a 50 m ELT, reduced and analysed, out to 20 Mpc for individual cluster members and between 10 and 500 Mpc for the properties of the integrated cluster. Based on individual stellar data, colour-magnitude diagrams (CMDs) and luminosity functions (LFs) were constructed and studied for age
parameters. For the integral cluster data, we studied the cluster colour index (b-y). We conclude that with a 50 m AO ELT, turn-off point (TOP) determination in CMDs provide ages of excellent quality out to 8 Mpc, of high quality out to 16 Mpc and of reasonable quality to 20 Mpc. At this distance level, the luminosity function provides good support. The integral colour, (b-y), as an age parameter for the clusters, can be determined with high precision out to at least 300 Mpc and with somewhat reduced accuracy to 500 Mpc. Thus, using a 50 m ELT and observing stellar clusters, we can study evolutionary parameters of galaxies out to 20 Mpc and obtain age parameters out to around 500 Mpc from the Sun.