I was a bit older (32) when I was diagnosed with Psoriatic Arthritis. I went the non-medication route and got tested for food allergies. After eliminating wheat, dairy, eggs, soy, potatoes, tomatoes, peppers and red meat from my diet the arthritis went into remission. It did take a little while. (And the digestive troubles I'd been having cleared up too.) I ate that way for a year, until I had no joint pain at all and all my tests were normal (SED rate, etc.) I now eat strictly gluten free and avoid dairy and soy, but I'm pain-free and back to teaching PE and coaching basketball and doing an occasional triathlon.
It might not be scientifically proven, but it worked for me. The rheumatologists wanted me to take Methotrexate and Plaquinil and I just couldn't do it after looking at all the side-effects, which is why I went to the naturopath and went the diet route.
If you do have an autoimmune type of arthritis, the food allergy/intolerance connection may be very relevant.
Diagnosed with "Colitis", 1985. Later told I had IBS. Suffered for years until changing my diet.
Diagnosed with Psoriatic Arthritis, 1996. Went away after eliminating wheat, eggs, soy and dairy from my diet.
Diagnosed with Minimal Change Disease, 2003. In remission since 2004 after fanatically eliminating all gluten from my diet.