Multiple human genetic diseases are caused by mutations in the maternally transmitted DNA of mitochondria, the powerhouses of the cell. It is important to study how these mutations arise and accumulate with age, especially because humans in many societies now choose to have children at an older age. However, this is difficult to accomplish in humans, particularly for female germline cells, oocytes. To overcome this limitation, we studied mitochondrial mutation origins and accumulation with age in a primate model species, rhesus macaque. We found that new mutations accumulate the fastest in metabolically active liver and the slowest in oocytes. Thus, primate oocytes might have developed a mechanism to protect their mitochondrial DNA from excessive mutations, allowing reproduction later in life.