If you are looking to change this behaviour in vBulletin, there are three applicable settings:
Administrative:
Change the default thread cutoff for a forum via the Admin Control Panel :: Forums & Moderators :: Forum Manager :: Some Forum :: Default View Age.
User option:
A user can set their own "Default Thread Age Cut Off" in the User Control Panel.
One-time display:
When viewing a forum listing (i.e., the thread titles), you can change the default date cutoff, toward the bottom of the page under "Display Options".