According to Nutanix documentation on unified storage (NCP-US) v6, to automatically delete backups older than one year, an administrator should modify the existing bucket lifecycle policy to set the expiration period to one year. Lifecycle policies enable administrators to automate the transition of objects to different storage classes and to expire them altogether. In this scenario, modifying the existing bucket lifecycle policy to shorten the expiration period to one year will ensure that backups older than one year are automatically deleted to free up space in the cluster.

https://portal.nutanix.com/page/documents/details?targetId=Objects-v3_1:v31-lifecycle-policies-rule-c.html