Michael,
Firstly, you deserve a lot of credit for smartly thinking so far forward with your interest in real estate. I just turned thirty and am essentially in the same place as yourself in terms of deciding to invest. I wish I had an 11 year head start!
I have several things to add:
Hold off on the car, 450 is manageable but houses don’t nickel and dime you, they fifty and hundred you so to speak. If possible find a cheap grandpa car or truck, they are usually babied and meticulously maintained. It may not be sexy but it will get you down the road for a while. I have an old Prius and while it is bland and slow and totally uncool it will haul a good amount of stuff efficiently. This matters because you will do a lot of driving while finding then fixing your investment.
Regarding the military, I am currently Air Force reserve and also spent 4 years active. You will have many great benefits from serving, including a va mortgage, reliable paycheck and excellent health insurance. Additionally the friends you make are the best people you’ll ever know! It will be hard to invest while on active duty, 12 hour plus shifts are the norm and you may move around often or be tdy constantly.
I chose to be a jet mechanic when I joined at 19 and that job has provided me with the ability to have a good life both military and civilian.
I suggest focusing on real estate for now, see if you’re ready for the analysis and negotiating. The military is a big party so waiting to be 21 may be advantageous.
Either way, you’re doing the smart thing by asking and reading and responding! Good luck!