Google Script to Clean Inbox

clean.js

// Archive older emals
function ArchiveEmailGroup() {
  var Size = 100 // Process up to 100 emails at once
  var emails = GmailApp.search('label:inbox is:read older_than:14d'); // Archives 2 weeks old emails
  for (i = 0; i < emails.length; i+=Size) {
    GmailApp.moveThreadsToArchive(emails.slice(i, i+Size));
  }
}

//Mark old unread emails as read
function MarkReadEmailGroup() {
  var Size = 100
  var emails = GmailApp.search('label:inbox is:unread older_than:31d'); // Marks 1 month old emails as read
  for (i = 0; i < emails.length; i+=Size) {
    GmailApp.markThreadRead(emails.slice(i, i+Size));
  }
}