RDFDatetime at which the object was created.

def age(self):
    """RDFDatetime at which the object was created."""
    # TODO(user) move up to AFF4Object after some analysis of how .age is
    # used in the codebase.
    aff4_type = self.Get(self.Schema.TYPE)

    if aff4_type:
      return aff4_type.age
    else:
      # If there is no type attribute yet, we have only just been created and
      # not flushed yet, so just set timestamp to now.
      return rdfvalue.RDFDatetime.Now()