....the lower Enlisted ranks are all about time in service and time in rank....there are waivers to get early promotions if you meet the criteria and command wants to advance you - but that doesn't happen often....every NCO rank requires you to go before a review board....anything Officer will generally have higher academic requirements and you will have to go to a Military Academy just for being an Officer....your best bet, going in, is at least some college....doesn't have to be anything fancy....just a 2 year degree in whatever at a community college should be enough to get you in as an E-3 [actually for these purposes I think they calculate credits, not degrees]....a 4 year degree will get you E-4 rank coming in the door [which will definitely make a difference - especially in a combat unit]....
....but this is what I really wanna tell you....fukk all of that shyt....look into being a Warrant Officer....they are considered "specialized" personnel....they don't have to go to a Military Academy for Officer School....instead they receive specific training for their area of expertise....these are dudes who perform skilled work - but there just isn't a need for a large number of them....they commonly don't have active supervision and are trusted to follow orders and do their job [because there are not many of them and they are expected to be self sufficient]....