Recently I have seen a flurry of old questions being flagged as duplicates of newer questions. Surely this is the wrong way round?
Although logically this would be the norm, there are times when the newer question is either better asked, better answered, or both. That's my guide in proposing closure of older questions: which provides the best combination of question and answer.
See also the Meta post on this issue: Should I vote to close a duplicate question, even though it's much newer, and has more up to date answers?