I read the sticky in a couple different forum sections and it says do not revive a thread older than 6 months. However, I see threads being locked after being revived from a 3-month period of inactivity...

Which is it? I feel like 3 months is too short, but that's just me.

It really depends on the mod/admin, and in what section it's in. Normally in the sections I mod (the FF forums) I prefer to abide by a 'don't post if it's older than six months/not on the first page' rule, but lately I've been more lenient in that regard. It all depends on if the person reviving it has something relevant to say - if it's just spam or if the thread revived is from eight years ago then I usually just close the thread. But if it's a relevant post, I leave it be. :)

Okay. There are a few sections where there are threads substantially older than 6 months on the first page still.
Another possible problem I have with this is that the old threads' conversations may spark a new one. Some conversations may never have even happened if not for some people perusing through "dead" threads, but creating an entire new one just seems like it would clutter the place, and it would be awkward to create a thread in response to an old one.

Anyway, just my thoughts. Do with them what you will, and thanks for the response.

EDIT: I should add that I'm fully aware that there are times when it's obvious a necro-posted thread should be locked, such as some oblivious person going through and posting lame single-sentence responses in multiple threads that died long ago, and for a reason.

Most of the threads I've closed in the General Gaming and Role Playing Sections, were revived after lengthy periods of inactivity. Some which are older than six months from their initial post are active, hence are not closed. It is a personal peeve of mine, when I see a thread revived without valid reasons or merely doing so to generate a post count to enable the PM function (more than likely just to send PM's to people with upload links, to leech MP3's etc... another one of my personal annoyances).

Be thankful this forum doesn't have the rules towards thread necromancy as some others... revive a dead thread and your account is deleted automatically.

If the topic is one you feel deserves a response, well the person who you'd be responding to, more than likely will not respond because, as I said above, the people asking the question no longer come here so there's no point in responding. However, if you do have more information, then by all means make a new thread with General information towards the game in question.