21 years old, extremely unstable employment history, bad credit history with proven financial irresponsibility, and generally discharged as well as poor performance by your own admission while active.
I'd say right now would be a big no-go. Get a job and STAY WITH IT, clean up your credit history, and try again in 6-10 years. I know 30 sounds an eternity away, but you've got a LOT of work to do before any agency I know of would even consider you at this point.
"Now I can just tell people that I'm old, cranky and to leave me the hell alone!" --retdetsgt
"I'm a certified Bovine Scatology Detector" --Creeker