WatchDirectory Professional can detect files and directories based on their age (how old they are). This allows you, for example, to delete files older than 7 days using the Delete Files plugin. Or to send an email for those old files to help you remember to "process them".
An innocent option
When you configure WD to use the "File Age Monitoring Method", one of the options you can select is Remember triggered files. If your task sends an email for "old files", you will want to select this option as it will prevent multiple email messages for the same file.
However, if you configure a task that will delete, move or rename the old file (the original "old" file does not exist anymore), make sure you do not select this option. The "remember triggered files" option stores info (filename, timestamp) into the history database for this task and this is totally unnecessary if the detected file is gone. While the history database will "auto cleanup", this file age info can use a lot of diskspace (for large directories) and cause your task to run slower than needed.