If you mean for a specific folder only, then I think there are are at least two places where you can do this, but I have done it sucessfully this way:
In ESM, expand the Server, then the Storage Group, then the Public Folder Store.
Select Public Folders in the left hand pane, then in the right hand pane, right-click on the public folder you want to edit the settings for, and select Properties.
Click on the Limits tab then under Age Limits deselect ‘Use public store defaults’. You can then set a time limit (in days) for the items in that folder. This worked for me.