I don't think it is terribly helpful to comment on very old articles. I like blogs with comments because they keep the author honest and because they provide relevant pointers to other readers of the blog. Comments on new articles work well for that. Comments on old articles, however, aren't seen by regular readers of the blog. They are only seen by the blog author and by the other people who commented on the same article. That goal is better served by plain old email.
As such, I am going to reject comments on articles more than a month old, as a matter of policy. I would like to make that automatic, but I don't see how in Blogger's settings. Does anyone know how? For now, I'll just do it manually.
My apologies to people whose comments are dropped by this policy. I do read them, and I take them as a suggestion on what to write about.