A milf who used to be hot but has become too old and loses her milfness, past her date with which she can still be a milf
Guy 1: Hey check out the milf down the aisle, I really want to get with her

Guy 2: Hate to break it to you but shes past her Milf-by-date
by milfs at the gym October 12, 2010
Get the Milf-by-date mug.