This 2010 question and this 2014 question are identical. Both have a significant number of upvotes and well-received answers. Should the 2014 question be marked as a duplicate of the 2010 question now in 2018?
One should probably be closed as a duplicate of the other, and then the duplicate's answers merged with the canonical question. Which one is mostly a matter of which question is better posed. (A impending merge means which answers are better becomes academic.)
The cleanest way to do this is for someone to case a duplicate vote on the one they think merits being the canonical one, and see if the community agrees enough to give their close votes too.
I don't have an opinion either way — but I can say that, yes, it's fine to close a 2014 question as a duplicate of a 2010 question (or vice versa), even four years late. :)
Moderation is timeless, so we act on closures regardless of timestamps.
A couple of people happened to nominate the 2010 one as a duplicate of the 2014 one, and I'm inclined to agree. In general 2014 content toes better to current quality expectations than 2010 content.
I'm personally disinclined to merge them though. The answers in the 2010 question were before some more recent standards (such as Should I be requesting people answer the question independently?), so I'd rather leave the collection of "what about this one very specific thing I'll just mention vaguely" answers behind in the old 2010 question. I'd be more inclined to post a +500 bounty for a comprehensive answer on the new 2014 question.