Yep, case-by-case for me too.

If someone revives a two-month-old discussion of religious ethics in EoEO, I'll leave it open. If they revive a two-month-old EoEO thread on "I'm seeing this girl tomorrow, how do I ask her out HELP URGENTLY!", then chances are it's gonna get closed because there's just no point.

Likewise, if I'm trawling through the FFX forum and find that someone's posted in a year-old topic like "Shlup vs Lulu: who has teh hotest buns!?!?!?" I'll dispatch it with extreme prejudice. A discussion of "the importance of religion in Spira" or "good strategies for defeating Penance" is far more likely to remain open.

Sometimes, automatic thread closure would be a good idea. However, there are always exceptions, so a more discretionary approach is needed. The aim of the forums is to help people have interesting, creative discussions; threads should be left open or locked accordingly, depending on their content and level of relevance.