1) In my own experience, old "evergreen" articles (updated if necessary, left alone if not) can rank extremely well in Google.

2) If Google already has your old blog posts in its index, removing date/time stamps won't fool the algorithm into thinking the posts are new.

Don't hide the date.

I hate it when I am searching for an answer on, say, a software forum.

You find the answer, but don't realize that it is from three versions prior of the software because there was no date at the top of the article / post.

Besides, it would look a bit fishy if an article claiming to be from 2014 had attractive backlinks whose own dates range from 2006 to 2012.

In my experience, articles pre 2010 are useless now from Google point of view.
The move become very aggressive since June 2014.

I've conducted a research in my DB and articles pre-2010 not having almost any hits.

The same is about forum content.

I've conducted a research in my DB and articles pre-2010 not having almost any hits.

We've had the opposite experience: Some of our most popular articles date back 10 years or more, probably because they've acquired a good many links over that time.

Regular updates can keep an article relevant, and some topics are "evergreen" and up to date even if they're left alone. (For example, a decade-old article on how to fry fritters or the life of a 14th Century saint probably wouldn't need updating very often unless tastes in cooking oils had changed radically or new historical facts had come to light during the last 10 years.)

Also, the structure of a site could have an impact on how much freshness matters. Is the site organized by topic or category, or is it in reverse chronological order, with older articles or posts being shoved to the back of the queue? For that matter, who's to say that Google may not weight "freshness" differently (if at all) depending on whether a site (or page, for that matter) is perceived as being a blog, a news site, an evergreen information site, an e-commerce site, or whatever? We have no idea whether that's the case, but it would be a reasonable approach.

As for the question of whether to use date/time stamps, that probably depends on the nature of the site and the content, too. For an evergreen article, a "last updated XX/XX/XXXX" line at the bottom of the page may make more sense than a time or date stamp, if it's needed at all. (That's the approach used by Wikipedia.)

Yes, it depends on the site, but in the last few years I've seen an explosion of new content.
It's hard to have popular and evergreen articles.

In the news category, the content is getting old very fast now.
It's "interesting" to see how a story rose in Google News on a small site and in a few hours, even days, the big sites will get the first spot.

Is the same in SERP, but on a larger time scale.

As I told you, my CMS is registering hits/article/day.

I have on a site more than 300 000 old articles (pre-2010), but it only brings now ~ 1000 visitors/day.

I can rarely see on my "internal top" articles from 2012.

If you look up {single word}, one of the top five hits is a page that says, in paraphrase: "This page was created in 1997 and hasn't been updated in years [the 'last updated' line says September 2011], so you'll have better luck somewhere else".

I guess that means that sometimes age trumps everything.

I guess that means that sometimes age trumps everything

Try telling an employer that LOL

Most annoying is researching a technical issue and not finding a date stamp. I do not know when the article was written and whether newer information might be available that I should research.

Regarding changing an older page that is timestamped to some newer date, I have not noticed that my "evergreen" pages suffer in the SERPs because of age.

In the case of one article I wrote, the article -- though many years old -- is part of the curriculum of a course at a major West coast university. At the time I wrote the article, the information was based on best available evidence and was relevant for the issues of the time. No need to update it.

I personally did not see any traffic changes after removing timestamp for the articles. I however did receive more complaints about outdated information.

So I think better to keep the old timestamp unless you do actually want to update the old articles to make them current.