Hm.. 18 -Can- be do-able but the only way I can find around it is that before you were too unstable and the government only offered you a place if you got off drugs, then they'd offer you to Military and provide a drug free haven? Does that sound about right? But if you join at 18 you wouldn't be able to become a veteran til 28 and your character's 26. 

And yes, you're right, there is a lot to be done on the first post, It's a pretty basic "cut-out" on what I want, I'm fleshing it up now.