Diabetes mellitus continues to present a large social, financial and health system burden across the world. The relationship between age of onset of the different types of diabetes and all-cause mortality is uncertain. In this review paper, the relationship between age of onset of the different types of diabetes and all-cause mortality will be reviewed and an update of the current evidence will be presented. There is strong evidence of the relationship between age of onset of type 2 diabetes mellitus (T2DM) and all-cause mortality, good evidence of the relationship between age of onset of T1DM and all-cause mortality and no evidence of the relationship between age of onset of gestational diabetes or prediabetes and all-cause mortality. Further research is needed to look at whether aggressive management of earlier onset of T2DM can help to reduce premature mortality.