He is saying that if someone posts in an old topic, their post would be automatically sent to an admin for approval. The person doing the posting wouldn't have to do any pm'ing.
More straightforward to just have threads lock themselves after a couple of months of inactivity.
Or we could just ban violators since, you know, that's been working for the past 6 years.
Especially considering there is no such thing as an automatic thread expiration plug-in for Invision Power Board. Trust me, I've looked.