I think a year is good. But I would have an exception that allows the OP to continue to post later if they have an update. I appreciate someone later responding with an update after we have provided advice and suggestions.

I would also allow someone to edit a previous post that they made, but that is not a new post and does not show up as such. For example I had a suggestion that I made on maybe four or five posts on some equipment. And then a few years later had a catastrophic failure, so I went back to my previous posts and added an addendum. And also private messaged those that had responded to my posts where I had a bad suggestion.