Personally if someone reviews one of my old questions and teaches me something new I would be as grateful as if the question were one day old.
Again the age of the code or question doesn't matter, I could have been making the same mistake since 2014!
Now hopefully I've not been so silly to have made a mistake for so long, but how can I know that if my question has been closed?
My opinion on the matter is very different than yours:
Personally, if I wanted a code review of a 1-page code snippet in 2014, I would not still want a code review, so I also don't review these as a reviewer.
Our close reasons exist to fix problems.
Our no. 1 reason, Code Not Working As Intended, is a key close reason and stops our site from become Code Debuggers or Stack Overflow+.
Our Author or Maintainer close reason helps prevent our answerers from legal and moral quandaries.
If someone illegally posts code under the wrong license we'd rather our answerers not to get in trouble.
Additionally, we had someone come to our site asking for a review of some code to determine if someone should be fired!
We as a site decided to not condone this.
But your suggestion is to employ symptomatic fixes, not root cause fixes.
the reason I care is that I use the unanswered questions list as a "TO DO" of things to review. Arguably, I should do something else
Yes the issue is SE search or your workflow, not close reasons.
I understand that there's instead a push to review all of these, but I admit I don't really understand why.
The issue then should be why we have zombies and how to stop questions from becoming zombies, not how to kill them once they've become zombies. Or to question our push to review zombies.
Stack Exchange is intended to be a searchable resource for everyone.
Have a question? Google it and read the Stack Overflow/etc. answers to fix your problem.
I've only ever posted a handful of questions on Stack Overflow, but Stack Overflow has answered thousands of my questions.
Now you could argue Code Review isn't like Stack Overflow.
However I've had answers be upvoted years after the question was active because of this.
So my answer was helpful for someone who wasn't the OP.
As such your reasoning doesn't take into account people who aren't the OP.
And moves away from the Stack Exchange model.
I appreciate your anecdotal evidence is different than mine.
However your anecdotal reasoning doesn't match the Stack Exchange model or the reasoning behind our existing close reasons.
Additionally your suggestion will impact users (like me) and cause them to have a negative experience of the site.
For what benefit?