SyncFF is a drop utility app and service for setting the modification and creation date of folders to the most recent modification date of their contained files (and, optionally, folders.) This way the modification date of the folder matches the modification date of the "youngest" file (or, optionally, folder) it contains. The process is recursive, so all subfolders are processed.
SyncFF is part of the Limit Point Software Utilities bundle. See http://www.limit-point.com/Utilities.html for more information and a list of currently available software. A single donation activates all utility programs, and all upgrades are free and new products are included.