Does anyone watch Parenthood? I don't. I only watch Food Network. But, I did see a few clips of the last episode where Max overheard his father shout to his uncle that he has Asperger's. Later, sitting down with his parents, Max asks what Asperger's is, and his parents fumble around trying to explain. His mom cries. Max leaves with not much better of an idea about what he has, other than that he doesn't know anyone else who has it and probably feels very alone.
So now that we all know how not to tell your child about their autism, how do you do it? I'm just going to give you my take on it. You can take it, or leave it, or change it, or whatever you want to do with it, but this is what might have worked when I was younger.
"One of the best things in the world is that everyone is different. There are no two people alike (personally, I would say something more like 'God has created everyone differently,' but do with that what you will). We are all good at different things. Some people are really good with their hands, and they might become artists so that everyone can enjoy their beautiful art. Other people are really good writers, and they write books for everyone else to enjoy. Some people's brains make them really good doctors, and they help others by healing them. Everyone who meets you knows that you're really good at learning about different dinosaurs (random skill), so maybe one day you can be a teacher and teach people about dinosaurs. What are some other things you're good at? (let the child answer)
"Everybody has different things that they need help with, too. (random example) Do you remember when we painted the living room? I needed help from your dad to reach the high spots and put on the new wallpaper. That's okay that I needed help. Sometimes you need extra help knowing what to say to your friends (or staying calm, or sharing, or learning at school.... whatever applies), and that's okay too. We all need help with some things.
"But here's the really cool thing. Some people are a very special kind of different. These people are often really smart. They're really good at one special thing, like you and your dinosaurs. These people also might need some extra help to make friends, talk to other people, (insert things your child needs help with here). Doctors say that people like you, who have these certain strengths and weaknesses, have something called an autism spectrum disorder. There are a few different kinds of autism. The kind you have is called (insert specific diagnosis here, if you want). People can have a little autism or a lot and need a little help or a lot of help with different things.
"It's important that you know that autism is not a disease. In fact, it's not even a bad thing. It just means that your brain works differently than most people's brains. All of us in your family and your friends think that autism is pretty cool, because it helps to make you who you are. Some people with autism have done big, important things, and someday you can do those things too. That's what parents, teachers, and doctors are here for- to help you to be successful.
"Do you have any questions about what autism means or how it affects you?"
Personally, I could have handled this conversation by preschool age. I might have done better if my mom wrote it down and allowed me to read it, then gave me as much time as I needed to process and ask her questions. I remember when my mom had the other Talk with me (haha, I know). I was about 5, in preschool, and she didn't hold anything back. She gave me twenty four hours of time with her to continue to think and ask questions, and she answered every one. Do not rush your child. Allow him to think and process as long as he needs, then make he knows that he can continue to ask you questions for... well, forever.
Again with the "personally," I feel that a child should be informed of his autism by school age. If this conversation isn't age appropriate for a 5-year-old, either let me know and I'll see what I can do, or do what you need to do to make it fit your child, but please do not continue to hold off on letting him know because you don't know what to say or because he hasn't asked questions. If you wait for him to ask, it means he may have been ruminating on the issue for a long time and has finally decided to ask. You don't want him to wonder and worry about why he's different.
Of course, children are totally individuals, and you have to do what's right for your child. There's no way I can say that "age five is it," because each child is different. You know your child best.