[revvx]

The metric isn't exactly "newness" but relevance.

Timeless or "evergreen" content doesn't have to be updated. It's alright to keep them as is.

But keeping obsolete content online is a pain in the ass for users, so they will increase your bounce rate. Either update them or show a big notice on the top with a link to a newer article. Google will hopefully pick them up and the internet wins.