The GRE, which was first administered in 1949, is four years

With all due respect to GyanOne, I disagree.

I believe this question is fundamentally flawed. In my reading, (B) is 100% correct. The subject is not "the GRE's age", but rather just "the GRE". If we drop the modifying clause between the commas, (B) becomes:
(B) The GRE is four years older than the GMAT.
That is a classic correct comparison --- noun to noun comparison. Adding the modifier doesn't change anything. (B) is 100% correct. In fact, (A) & (C) are also grammatically correct, although a bit wordier.

What is the source of this question? Keep in mind that not all GMAT SC practice questions are created equal. Some are excellent --- for example, MGMAT consistent produces high quality questions. Many, even from companies with reputable names, are absolutely atrocious. If I had to give the question writer a grade for this question, I would give an F. This is an abysmal failure of a question.

In a true GMAT SC question or a high quality practice question, there are clear grammatical errors separating most of the incorrect choices from the correct choice, and the wordiness/concision thing is usually not used as a split for more than one answer.

Here's a high quality question, a practice SC question dealing with comparisons:
https://gmat.magoosh.com/questions/3229
When you submit your answer, the following page will have a complete video explanation. Each one of Magoosh's 700+ GMAT practice questions has its own video explanation, for accelerated learning.

Let me know if anyone reading this has any further questions.
Mike