As questions age, they increasingly are pointed to as the source for duplicates of new questions. Should the older questions be reviewed for closure as well to make sure they are not limiting new content.
In a similar discussion on meta http://meta.stackexchange.com/a/3023/178816 (dated 3 years ago but still relevant in this case), shog9 points out "If a new question is answered by the answers to an old question, I will generally consider it a duplicate.". This is a good point.
However, many of the "old questions" are links. And many times, the link does provide an answer to the situation, albeit dated and increasingly irrelevant.
Moreover, I find it surprising that if a title shows up which is similar to the current question then that is immediately marked as duplicate often times when there is only one answer in the duplicate question. People wanting to know the answer to a hard question should not be punished for the ease of which others will give up on their question.
In this newer question Closing posts as duplicate of very old questions Josh Caswell points out "Older questions have often accreted lots of useful information". Although many questions have accrued a large wealth of useful information, they tend to not be the questions which come into question because they are on common or well known topics.
My main point is this: technology moves very quickly, and often new solutions trump those of the past few years. Even if a duplicate question has a suitable answer for that scenario, it does not always mean that that is the only bar none way to accomplish the goal.
Stack Exchange should favor new content and new approaches over deprecated ideas. Should questions which already exist and are flagged as the source of a duplicate be reviewed?