BC,
is your aversion to the 'strict discipline' of the forces an opinion borne of personal experience, or an assumption based on your presumption of what the forces are like?
I ask because, as the least military person you could ever hope to meet (ask anyone who knows me!), I had 22 years of wonderful times in the RAF. No ground tours, 7000 hours worldwide, enough social life to fill a couple of books, etc, etc. Sure, I clashed somewhat with the more disciplinarian members, but my professional ability and general laissez-faire attitude got me through most scrapes. I loved it - and now I fly 747s for Virgin (still....!). Don't rule the forces out until you've looked closely into what they can offer, and what other people your age feel about the job. And, as Send Clowns says, get more opinions about your knee problem; it may not rule you out.