Agreeing with Gerald about the "Don't touch it/Don't do it", i can add that you could simply modify the proper template in order to add a column like "last action date" and populate it with the field of the database that storest the last changed date (sorry, don't remember the name of the field right now). Better avoid to "change" an existent part of the system. Let the "Age" remain the age as otrs considers it.
But the points listed by Gerald are something I never thought about and probably are a good alternative.