Is it OK to close older questions as duplicates of newer ones?

Question

Example: Dwarf Alberta Spruce Winter Burn [duplicate], posted on Apr 28 2014 at 2:44, as a duplicate of How to heal this needled plant?, posted May 9 2014 at 16:37.

I had always thought the newest questions should get closed as duplicates of the older ones. Am I wrong?

I thought it was a mistake, so I flagged it to get switched, but the flag was declined, with the message:

flags should only be used to make moderators aware of content that requires their intervention

Which intervention I thought was necessary.

Answer 1

I've found that the question has already been answered on meta stackexchange: Opinions on closing an older question as a duplicate of a newer question [duplicate]

The highest voted answer, by Gnoupi:

No matter which one came first, the most relevant one should be left open, and the other one closed as duplicate.

And the accepted answer, by Bill the Lizard:

Most of the time double posts by the same user are caused by back-button edits, so the newer question is the one the OP really wants to stay. Even if the questions come hours or days apart, I'll usually elect to keep the newer one, since it will typically have more/better content.

In the case of duplicates by different users, I do take the dates into account. The older question usually takes precedence, if all other things are equal. The quality of the newer question can definitely sway my decision though.