Why are new users allowed to post late answers to questions from so long ago? Most of the times it's not even useful and it clutters up the Top Questions page.
I don't have the stats to support this, but I honestly don't know if I'd call late answers to old questions mostly not useful. Whenever I review late answers, there are maybe two or three out of twenty that are worth deleting (because they're not an answer or just poor).
But all the other answers have a right to be there and shouldn't be blocked just because there is a possibility the answer might be bad. If you asked a question and waited for a solution, would you appreciate having your post locked (even passively) and risking that the only person who knows the definitive answer can't even tell you because they first need to gain some reputation?
I'd find that frustrating, both
- from the side of the person who asked the question – because they might miss a helpful answer and don't even know – and
- from the side of the person who answers – because they think they have something to contribute (otherwise they wouldn't care to sign up) but are hindered.
I think we have good enough review processes that clear out unnecessary answers. There aren't that many "late answers" and they can be easily reviewed by our moderators and people with access to the review tools.
Also, as @nhinkle said, some questions that attract bad answers are protected anyway.
Some questions/answers are not static meaning that over time a better answer may surface. Since we encourage posters to search for previous answers, it seems we'd want to allow new answers to old questions.
I recently stumbled upon a 2 yr old AD question where a new answer represented a change in technology since the original question was posted.
Well, consider this question.
It was asked July 22 2009. Notice when the correct answer arrived -- April 11 2010!
So by your logic, we should have shut down that question after a few months and we never would have gotten an answer...
Eventually, though, another option is to not allow (somehow) new user to post answers to (somehow) old question with accepted answers.
As I remember, while I worked for a BBS in the telephone era, the rule was that however old you are in the system, however old posts (the ratio could be adjusted, obviously) you could reply to and thus raise its discussion. It may not be 100% appropriate (or even 1% appropriate) here, but it's a bright idea.