Unfortunately there is no normal with this awful disease. On the upside he is young, a full recovery is possible but will take time, perhaps years. It affects people differently which is why there is not a clear pathway to full recovery. I am sharing a link to a video presentation that is very informative on where the Dr's have found ways to improve care to make full recovery possible for everyone. I am hopeful this provides you with the knowledge needed to understand what the Dr's are saying when you visit them for progress updates. I would also encourage you to ask the Dr's to prescribe water therapy for your son, I go 2 to 3 days a week and it remove sgravity, which in turn helps me to move more freely. I am also including a link to a Facebook group that is safe and helpful to chat with others who are in the same battle as you.
https://www.youtube.com/watch
https://www.facebook.com/groups/gbscidpwarriors
What ever you do, never give up hope, some days it's all we have and it will never disappoint. Romans 5:5