Will I be able to join the USAF?

your only issue is physically, you gotta strengthen your joints and limbs... wall sits will pretty much cure your knee pains as long as you have never seriously injured them... you probably will get shin splints too, so its as simple as sitting with feet flat and lifting your feet up repeatedly while your heels stay on the ground... ankle do calf raises on something elevated 4 inches off the ground... be gradual when starting these exercise even though simple if you neer done them before you will be very sore... aslo for knee pains its usually from bad tracking, wall sits correct the tracking, but you should also do isolated squats with feet pointing out... on for your arthritis thing... yoga plain and simple.... if your not over thirty it means your just not active, not arthritis, maybe more tendonitis than that... okay and now i wish you good luck, its gets old typing the same things over and over again.... oh and once you get all these simple exercises pretty much in the bag, just and ankle weights or weight vest...