If you want, you can turn off comments on all entries older than 30 days using the following SQL:
update mt_entry set entry_allow_comments = 2 where
TO_DAYS(NOW()) - TO_DAYS(entry_created_on) >= 30;This closes comments on all entries 30 days old or older. Most comment spams are on older content, which are also less likely to have legitimate comments so this isn’t a bad option. You can run this yourself manually every week or so, or you can add it as a cron job
from BurningBird