My son has autism as well. He’s only 4, though, so we’re not at the stage you are at
Your son must be very high functioning for you to have been able to not tell him yet. As my son still doesn’t talk yet and has therapy daily, I imagine for us it will be one of those things like the fact that he is a boy – he’ll never recall not knowing about it. It’s such a part of our daily lives that we cannot really avoid referencing it.
I do agree with the general consensus that you ought to tell him. Waiting for him to figure it out on his own has too much potential to lead to resentment for not telling him. It is far preferable for
you (and your spouse) to control the method and environment that he learns about this than for you to leave it to chance and then be cornered by surprise one day and not know what to say.
How you go about it is going to be important, though. As kids with autism vary so greatly, your best bet is to speak with any therapists that work with your son on a regular basis or an organization like Autism Speaks and get some feedback. You know your son the best, so you are really the best one to figure out how to use that feedback to formulate the best plan.
This is just my take, so it may not be the best approach for you, but I would do my best not to make it into some super serious big deal. His brain works a little differently than most people. That’s not necessarily a bad thing. But it comes with its own challenges that it’s best for him to be aware of so that he can learn how to handle the differing expectations of others.
I would also say it’s important for it all to come from a spirit of love for him as your son rather than a judgment on him being different from “normal” people. I’m sure that goes without saying.
I’ll say a prayer for you and your son. Please pray for me and mine, too.