It is generally assumed that the Universe is homogeneous at large scales and that it can be described using Friedmann models. So far this assumption has served well and led to a good understanding of many features of our Universe. However, we should not forget that homogeneity is indeed an assumption that should eventually be checked against observations. While isotropy of the Universe is relatively easy to check, the radial homogeneity has many intrinsic complications. The assumption of homogeneity underlies so much theoretical and observational work, that there is a real danger of a circular argument. Consequently, any proof of homogeneity must ensure it does not rely on results obtained using an assumption of homogeneity. During my talk I will present how the assumption of homogeneity can be tested using luminosity and age data. The constraints from the available data will also be discussed.