I’ve always advised that there are three reasons to join the military: you feel an actual calling to do so, you have a family and no other way to support them, or you don’t know what to do with yourself so you have Uncle Sam take care of you for four years so you can work it out. (I was option three: I ended up staying for eight.)
I would also advise my kids or anyone else to only consider the Air Force, the Space Force (even though it’s still in beta) or the Coast Guard: while there are dangers with any branch, it seems that in-country if the bullets or IEDs don’t kill you quickly, exposure to burn pits and other toxins will kill you slowly.
The next set of the Mistborn saga would be a natural choice. You may need a period of adjustment for the first couple of chapters–it’s centuries later than the first trilogy–but I think you’ll really enjoy it! Wax and Wayne are great characters.