code: def DeleteOldRuns(self, job, cutoff_timestamp=None, token=None):
      
      if cutoff_timestamp is None:
        raise ValueError("cutoff_timestamp can't be None")
  
      child_flows = list(job.ListChildren(age=cutoff_timestamp))
      with queue_manager.QueueManager(token=token) as queuemanager:
        queuemanager.MultiDestroyFlowStates(child_flows)
  
      aff4.FACTORY.MultiDelete(child_flows, token=token)
      return len(child_flows)
docs: Deletes flows initiated by the job that are older than specified.