It seems strange to place so much emphasis on IQ alone. Maybe the department was actually considering Robert Jordan’s combination of IQ, having a college degree, and being 49 years old, and knew they couldn’t mention his age?
It would also be more reasonable if Jordan had an IQ of, say, 180. But 125? That’s not so high that it sets you apart from average people. In fact, I find it hard to believe that there aren’t successful cops with IQs of 125, or higher.
Regarding the issue of smart people getting bored with the work: I again find IQ a poor predictor of this. Post office work seems pretty boring, and AFAIK the post office doesn’t screen applicants for being too smart. (Do any other employers?) I would think other, personality-based tests would be more predictive of that than IQ.