Several factors determine how fast one progresses in a defense forces career.
The first factor that determines how fast one progresses in a defense forces career is competency. The more competent you are, the faster your rise: especially in the lower rungs of the military career ladder. Thus, for instance, if you are in the Air Force, and you are a pilot, your competence at this task determines whether you are able to progress in your career and at what pace.
The second factor that determines how fast one progresses in a defense forces career is conduct. You have to remember that the defense forces are actually disciplined forces, where discipline is very greatly valued. Under that scheme of things, if you are not very highly disciplined, progression becomes a very tall order.
The third factor that determines how fast one progresses in a defense forces career is connections: that is, how well connected one is. This is because in most nations, progression in the defense forces beyond certain levels is a matter of political decisions being made. Thus, for instance, in some nations, it can be hard for you to progress beyond being a Major, unless you are connected to the elites in government.