It depends on the wiki. Here on Community Central, after a while, they started "locking" threads that were inactive for at least 1 month. In a handful of cases, that was too soon so they changed it to 2 months. In that case, it is possible for a thread to remain open as long as it has at least 1 reply every 2 months. Of course, this was on the legacy platform and there was a script to do this. Now there isn't. So whatever rule you decide on will have to be manually enforced.

So it is my choice?

Yes.

Okay I will do this.

Even here, some users think "necroposting" is posting on threads that haven't been responded to in just a day. Generally (not always) we try to take a month or two months until we lock a thread, depending on how disruptive or continuous it is on the discussion. If the original poster of a thread comes back a few months later with "I haven't had time but tried it, but it didn't work", we generally won't lock a thread. There is no real automated way anymore to lock threads and it's fully up to the administration of a wiki itself. You can do 1 month or 2 weeks on a wiki with a lot of activity, or maybe leave threads open on a wiki with little activity, it all depends on how you want to approach it.

Some wikis are against necroposting. I personally do find necroposting annoying and I do not stan it.

To elaborate on the "it depends on the wiki", it depends on the activity on the wiki. If you have around 5 new posts a day, bumping old threads is more annoying than on a wiki where there's one a day.

We have a rule that if the post is a week old (so when it has changed from the "X days ago" to a timestamp, it's too old to reply to. In the case that people do reply, we tend to give a message telling them not to reply to old posts and lock the thread. With our activity level, that seems reasonable (and sometimes even too lax) but you do what you deem best.