There is no written rule on what age the thread has to be to ignore it. Can you locate such a rule here on the forum or CoC?
I have another good example:
Recently playing against Ashe I felt that dynamite burn duration is too long. I did a search and found this existing topic:
Ashe’s dynamite is a bit too much
It fit what I wanted to discuss. It was 12 months old. My post on that thread is not “Necroing” the thread.
Necroing a thread is similar to “bumping” a thread I think. Spamming or using just one word for no reason to revive an old thread.
My post is not just one word and it had a good reason. The thread was brought back to the top for discussion.