enable comments on old posts?

Apparently somewhere along the line I set up my blog to disable comments on old posts — after X amount of days, the comment box goes away. The thing is, I would kind of like to enable comments on old posts again — but I can’t find out what I did to disable them! I thought it was the autoshutoff plugin, but I don’t see that anywhere on my site. Then I thought it was Spam Karma 2, but I disabled that and the comments are still closed on the old entries.

Any ideas???