This searches for materials which have not been checked out since a particular set date, in a given format. Note that the proper format for dates is:
yyyy-mm-dd for instance 2012-03-16 for March 16, 2012.
Another method is used for reference books, where if they were added to the collection before a particular date, with that date given in the same format of yyyy-mm-dd for instance 2012-03-16 for March 16, 2012, or they have copyrights before a particular year in the format of yyyy such as 1975.
Please do not accept this as your only tool to select materials to be weeded. There are other criteria for selecting or deselecting books to be weeded, many of which are subjective. This list is only a place to start.