Echoing the other comments: Sorting your front page by "Active" tends to do that. I like sorting by "Hot" the most. You can change the default sorting on your settings page.
That's just gonna be at the mercy of how many communities you've subbed to and how many of them are active, then.
On my own "Subscribed" and "Hot" page I do get two posts that are over a year old, but most are still less than a few hours old.
My preferred strategy is to always browse All, and just block communities that I consistently dislike - once you've done enough blocking it becomes pretty great.