According to some sites i`ve seen around (I`ve researched this before lol), the main chick who sings the chorus agrees that its referring to a G6 pilot, which if I recall correctly is a high ranking pilot that pilots those fast war jets in the US military. so basically, the `fly` G6 is that super educated, ray-ban wearing, G6 pilot.
Going a bit off topic, to become a jet pilot in the military is one hell of an achievement, basically because you need to have a bachelors degree, then study another 4 or so years in the military, then pass a test to become part of a select few who will then COMPETE to become pilots.
Therefore, a G6 is pretty damn fly. I`ve had previous interests in joining the air force but, its been a while, so this information is not reliable.