Prune-locking?

[guspasho]

There's a feature that allows administrators to prune old topics from their forum, but I like to leave them available for posterity. However, I don't like when users or spammers in particular bump those old topics. It throws off the members. Can a function to lock all topics older than X days rather than delete them be implemented? And maybe with a checkbox list that exempts stickied topics and announcements?