function cleanUp() {
var delayDays = 7 // Enter # of days before messages are moved to trash

var maxDate = new Date();
maxDate.setDate(maxDate.getDate()-delayDays);

var label = GmailApp.getUserLabelByName("delete me");
if( label ) {
    var threads = label.getThreads();

for (var i = 0; i < threads.length; i++) {
  if (threads[i].getLastMessageDate()<maxDate)
  {
    threads[i].moveToTrash();
  }
}
}
}