So a Scout could zip through to Eagle really quick, say in a couple of months if he was really motivated?

Not really. Rank advancement in the lower ranks can be accomplished rather quickly. For instance the Scout Badge is fairly easy to achieve and can literally be earned in two meetings, because half of the requirements are met just by joining the Troop. The requirements for Tenderfoot, Second Class and First Class are a little bit more difficult, but can be earned in several months if a Scout is really motivated. Once a Scout reached First Class, there is a minimum wait of four months before he can move on to Star Scout, and that can be longer, because they have to serve in a Leadership position for four months between the rank advancement from First Class to Star, not to mention the other requirements they have to meet plus they need to start earning Merit Badges. In advancing from Star Scout to Life Scout there is a six month waiting period and again a leadership requirement and the same in going from Life Scout to Eagle Scout and again all of the other requirements they need to get signed-off by the Scout Master, an Assistant Scout Master or one of the Eagle Scouts.