This object indicates the age of oldest signature in the
sigblock. DRE stores the actual data as data units in the data
block and the metadata (chuck signature) in signature block.
If a new signature should be written to the sigblock when it is
full, then the oldest signature currently present in the
sigblock will be evicted. So this object would indicate the age
of the oldest signature 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.