Secondly, I think the 6months time frame given for a post that can be reported is not a bad idea, at that will give moderators less load, and ability to act on every report very quickly.
A spam post, low value post, off-topic post should be deleted whenever it is reported or seen by moderator. The age of that post is not important to decide deleting it or keeping it in one topic.
I disagree that limiting the age of post to 6 months + to consider deleting it or keeping it. Considering about its quality and off-topicness, contribution for discussion in that topic, and making a decision to send it to trash bin.