The estimation of age is an important aspect in osteoarchaeological analysis. In order to understand people and their fates in past societies, researchers must turn to palaeodemography. Therefore, it is vital that the methods of age estimation, which the foundations of palaeodemographic reconstructions rest upon, are as accurate and reliable as possible. In current Swedish cremation-osteoarchaeology, two methods of age estimation are commonly used: suture closure and relative thickness of the diploë. However, no substantial evaluation of these two methods have been undertaken. This study aims to evaluate the two methods of age estimation of cremated remains, suture closure and relative thickness of the diploë. This was done by testing the two methods on two unburnt populations, Mediaeval city-dwellers from Helgeandsholmen, Stockholm, Sweden, and Middle-Neolithic hunter-gatherers from Ajvide, Gotland, Sweden. Suture closure and proportion of diploë was observed in comparison with age-related changes of the auricular surface of the ilium and the pubic symphysis. Based on the results of the study, possible courses of action were proposed and then applied on cremated remains from a Late Iron Age burial ground on Lovö, Stockholm, Sweden. The results showed significant moderate correlation with age for both methods (0.61 for suture closure and 0.58 for proportion of diploë). However, early stage of suture closure could identify a group consisting of juveniles and young adults, while advanced suture closure could identify a group consisting of middle adults and old adults. These results, which proved to be more reliable than existing methods, can, hopefully, lead to improvements of the assessment of age in cremated remains, and increase our understanding of the fates of people of the past.