God bless you for seeing beyond this young man's disability to the real person he is.
As the mom of a 15yo who is severely, profoundly mentally handicapped it means so much to me when people recognise that my son is not just his disability. He is a whole person who has the same feelings and needs that any normal person has.
I just wanted to give a plug for the Special Olympics. It's a great organization. My son competes in the lowest level of swimming. These kids are the ones who often can't talk and who need flotation devices for safety. But if you've ever seen them in the water you would be blessed. They are so happy, smiling, flapping, splashing along like it's just the best thing in the world. These kids couldn't care less about a ribbon, it's all about the swimming and the cheering. Each one has a helper who gets in the water with them. The helpers are not allowed to push them along, but they can shout encouragement. It is a sight to behold.
If any of you ever have the opportunity to volunteer with Special Olympics, jump at the chance. You *have* to see the opening ceremonies. It's very much like the real Olympics where the athletes walk onto the field and the run, walk or wheel the torch in. I'm telling you, there is not a dry eye in the house. If you could see and hear and feel the enthusiasm, your life would be changed forever.
Thank you, OP, for telling your story. I know this boy's mother must be soooo happy that you have accepted her son. I would encourage you to find ways to letting this young man be a part of the department. It would make his day, and yours too.