Uptodateness and object_age are not stable
Both values depend on the time the workflow is run meaning that two users will get different values in subsequent runs.
Possible solution: calculate both in relation to a fixed date (e.g. use UNIX TS or seconds since 2008-01-01). This would though mean that the human readability/interpretability of the metrics is reduced (the value 10000 has no real meaning, currently it means 10000 seconds since last edit). It would also invert the problem of #2 (closed) so the object_age would need to be reverted (old objects have a high number).