Our daughter was around 9 when she was diagnosed. She had JRA. Just because they have JRA doesn't mean they will have RA. Most don't. Our daughter only has it in her left knee. When she was a toddler, she had a severe infection in her knee joint. We were lucky, she didn't have to have a knee replacement at that time or loose her leg. But that is what kicked it years later into JRA.
Unfortunately, she does have RA in that knee and will at some point have to have a knee replacement. It has been difficult. She had to give up a lot of things. Cheerleading, soccer, softball. She has flare ups from time to time and uses ibuphrphin (sp). She is 22 now. She does play softball but knows that chances are she will pay for it. She has a brace for the knee that helps. She lives her life. She is in college, was in marching band in high school (several flare ups but she wouln't quit!). She doesn't let it define who she is and what she does.
Follow the treatment plan. He should be better. Good luck!