This object indicates the age of oldest data unit in the data
block. DRE stores the actual data as data units in the data
block and the metadata (chuck signature) in signature block. If
new data unit should be written to the data block when it is
full, then the oldest data unit currently present in the data
block will be evicted. So this object would indicate the age
of the oldest data unit present in the DRE cache. It takes the
format of <x>d<x>h<x>m, where 'x' is an integer number. For
example, 6d20h30m means that the oldest data's age is 6 days, 20
hours and 30 minutes.