This isn’t much of a suggestion. We already try to lock it, but sometimes we miss one or two– we’re only human after all! The best way to prevent being punished for necro posting is... to not necro post. Check the date of the last reply and if it’s 14 or more days after, don’t reply to it. Message a mod on the forums and ask the thread to be locked.
I believe it is, but the forums are a little buggy sometimes so they don’t always auto lock, so mods have to.
Report their post. It violates the rules so they should not be doing it either.