I have been diagnosed with this, and now RA. My empathy and compassion go out to him. Help him to foster a couple interests that involve sitting, maybe even creating something for veterans, the homeless, or other disadvantaged people. Helping/loving people will resolve the inevitable hostility of being grounded when you want to move.
Father, we come before you on behalf of your child just getting this diagnosis. We ask that you strengthen your child, and especially these loving parents, and give them comfort and peace. Lord we ask that through this medical situation you bring this family closer together than ever before and never let them go asunder. We ask that you use our lives and our stories to be a testimony of your grace and glory and mercy. Lord, it is written "All things work together for the good of those who love the Lord and are called according to His purpose." We ask that you help us to always look for your purpose in every situation. In Jesus's name. Amen.

My son was also diagnosed with degenerative disc disease at 9 yrs old. I thought it strange that a young person could develop DDD. After further testing and an MRI, he was correctly diagnosed with juvenile rheumatoid arthritis, spondyloarthropathy subtype.
Both are treatable, but I completely understand your shock and sadness. Prayers to your son and family ❤️

May Jesus give strength and shine his peaceful healing light on this boy