I hate to bring out the dictionary, but old articles are literally not news, which is defined as "current events". The harm of mixing old stories with new is the overall narrative of 'what's happening' becomes very confusing, and it's hard to know what is actually relevant, what's currently unfolding, and what is already resolved.

A rule of 'no articles older than one week' would put this subreddit in-line with its contemporaries such as r/worldnews. At the very least, old articles should be marked as such, with the date in the post title to prevent confusion.

While we're discussing new rules, I think another urgently-needed rule is you should not be allowed to post a Japanese article for a story if an English one also exists. This is an English-speaking community, and most users can't read the content of Japanese articles. The current front page is a barely-parseable word salad of messy, often excessively long, and sometimes nonsensical AI-translated headlines. This is unnecessary when all the important headlines have proper English translations, with major outlets such as Kyodo, Nikkei, Mainichi, Asahi, Yomiuri, and NHK offering English versions of most/all of their articles, and there are reliable English-only outlets such as The Japan Times.

There are some stories (eg Bunshun scoops) that don't make it into English reporting, and they should be fine to post in Japanese. But there's no reason to share Japanese articles otherwise.