Remove old Drive files unless it has "#Indef" in its description.

DriveIndef.gs

var INDEF_LABEL = '#Indef';
  
var RETENTION_DAYS = 365;
var RETENTION_DATE = new Date();
RETENTION_DATE.setDate(RETENTION_DATE.getDate() - RETENTION_DAYS);

function DriveIndef() {
  var root = DriveApp.getRootFolder();
  
  RemoveOldFiles(root);
  Drive.Files.emptyTrash();
}

function RemoveOldFiles(folder) {
  if (folder.getDescription() !== null && folder.getDescription().indexOf(INDEF_LABEL) != -1) {
    return;
  }
  
  var files = folder.getFiles();
  while (files.hasNext()) {
    var file = files.next();
    if (file.getLastUpdated() > RETENTION_DATE) {
      continue;
    }
    
    if (folder.getDescription() !== null && file.getDescription().indexOf(INDEF_LABEL) != -1) {
      continue;
    }
    
    file.setTrashed(true);
  }
  
  var subFolders = folder.getFolders();
  while (subFolders.hasNext()) {
    RemoveOldFiles(subFolders.next());
  }
  
  if (!folder.getFiles().hasNext() && !folder.getFolders().hasNext() && folder.getLastUpdated() < RETENTION_DATE) {
    folder.setTrashed(true);
  }
}