I tell my 6 year old that everyone was made different (we are Christian so this part of the convo is faith based) and just like our skin, eyes, hair, and interests are different, our brains are different, too. I tell him that he was made super smart with dinosaurs but that his brain struggles when noises are loud and THAT IS OK. I always, always, ALWAYS focus on the stuff he can do when talking about his differences with him. It's cute, he'll tell people he doesn't like noises, lots of kids, or bright lights because he has autism. He also expresses when he is mad by saying that. I am a special ed teacher and am always trying to help my students with their disabilities by focusing on the things they are good at (keep high self-esteem if possible!) and that we work through what we struggle with. Hope this helps... sorry it is kind of a ramble :)

I have found that informing my son that he has Autism has given him a way to explain his "quirks". He was diagnosed at age 8-he's 14 now. It didn't really seem to affect him at the initial diagnosis, but as he got older and changed schools...puberty (need I say more!) it's given him a sense of security knowing there's a reason he's different. He doesn't go around announcing to everyone that he has Autism, but he seems to understand that he does things differently than his peers.
I also helped him write a Social Story to share about Autism with his peers. I know!-a Social Story for neuro-typical people. CrAzY! It's designed specifically for our circumstances and how he may respond to specific situations. It gives him confidence to be able to share it without having to stumble over words or forgetting something he wants to share.
We too are Christian and have explained that God makes everyone different. He has gone with the youth group on retreats out of the city and summer camp out of the state.
I also am an instructional assistant with special ed kids in 7th and 8th grades and in the school he attends. I literally bring my work home with me!

My son is also high functioning but he does realize some things about him are different - mainly his speech. Personally if your son doesn't think he is different I don't see any reason to point it out. If he ever asks why he does things differently than other kids then you can explain it to him.

when we told our son about his high functioning autism we tried to stick to his strengths and weaknesses. we told him that every kid was unique, with their own gifts and challenges. we gave examples of both and said there were other kids like him too. he was old enough at the time (8) that we discussed the label (high functioning autism) with him and we said that we were trying to help him not be so anxious and we were going to work as a team to help him understand himself better. i don't recommend using the term "disability". that accidentally slipped out in conversation not too long ago and it was a huge blow to him. we had to back track and repeat our conversation from a few years ago to reinforce that he was not broken or deficient, but different in a good way. he has some amazing talents and he's so smart, but it's just the little routines of daily life and school work that make him anxious and frustrated. thankfully, he handles it pretty well, but we've had to keep reminding him that our goal is to see him more comfortable and happy.

If his friends do ask or if you believe it will help, something that was a great help with my son's 1st grade class (he's now almost 16) was to have a story time where a picture book that his therapist helped us make was discussed when he was not in the room. It described in easy terms what autism was and how it sometimes made it hard for him to have a lot of commotion or to think of the right things to say or to sometimes say things that might seem different to them. It pointed out the ways that he saw the world or interacted with the world that might be different but also the ways that were the same and ways that they might be able to help. It also explained that when he might do things that could be hurtful to them, that he didn't necessarily mean it, that sometimes he didn't think of how what he did might hurt others feelings and that he hoped they could understand and work with him to try to be his friend.