I generally agree with FF.
Perhaps one scenario in which GMAT "aging" might have some influence is if, say, your GMAT score were lower than you would have liked, but you subsequently demonstrated in other ways that you improved in the following years on the dimensions in which you did not perform as well GMAT-wise. In such a case, some AdCom readers might give slightly less weight to your GMAT score.
It all ultimately depends on context.
At the end of the day, take the GMAT when you feel you are most prepared - within the five year validity period. That is the most important consideration.
PS - For many people, taking the GMAT while working full-time in a time-consuming job can be stressful; it is not a bad idea to take the GMAT while you still are in the "student" mindset and have the student timeframe.