First and foremost. Sit down and shh. Don't try to insist on helping him, don't hover over him, don't constantly remind him that you're there to help him.

Let him grow with indepedence and exist knowing that if he personally feels he needs help, he can ask. Otherwise, he should be free to move and interact with the world at his own pace and leisure.

I have same diagnosis, but only declared so back in 2017. I'm in my mid-30s, so got to live 'normally' for most of my life which probably helps my transition easier.

Which does bring to mind one thing.. Colors. He will definitely have trouble with colors and not recognizing what is supposed to be a proper color for something. Having experienced life growing up with normal vision, I know what things are supposed to look like even if my eyes are completely garbage about telling me the truth now. With him being so young, he isn't going to have that experience to fall back on and I would imagine he'll need help often with that.

Just interact with him. Let him know, even if you aren't saying anything to him directly, that he isn't just a random person sitting in the room while others do things. You can do games and socialize with him.

Which leads into my final, biggest point. Don't get set in a mentality of thinking this is the end for him. He's fine. 'Nothing is wrong with him' essentially. I still do plenty of the same things as my peers and others do, just with slight difficulty/augmentation of method. It's not a death sentence on life.

You'll be fine with helping him out, already showing that by posting here.

Feel free to ask anything, but I think the first thing you need to do is just calm down and realize it's okay.