code: public long getCumulativeVmem(int olderThanAge) {
      long total = 0;
      for (ProcessInfo p : processTree.values()) {
        if ((p != null) && (p.getAge() > olderThanAge)) {
          total += p.getVmem();
        }
      }
      return total;
    }
docs: Get the cumulative virtual memory used by all the processes in the
  process-tree that are older than the passed in age.
  
  @param olderThanAge processes above this age are included in the
  memory addition
  @return cumulative virtual memory used by the process-tree in bytes,
  for processes older than this age.