In Carter years it depended on MOS, I could not get promoted in Admin so I went Avionics and made E-4 almost overnight and E-5 two years later. I ran into Admin Marines I knew still stuck at E-3 or E-4. It was really all about getting into a technical MOS back than.
Combat Arms..get some rank..change to Admin..get assigned to the Special Management Command. Requires high test scores..some college..attention to detail and the ability to work alone.
today..have no idea if the requirements have sunk..