DS10 and I have talked about this a lot. I encourage him to give whatever answer seems "safe" considering his relationship or comfort with the person who asks. Sometimes he defers to me. Sometimes he says his b&m grade-skipped grade. Sometimes he replies with his age. Sometime just "it's complicated" and if that gets a curious response, then "he's homeschooled". Homeschooling is fairly common around here so that is usually an accepted end to the conversation.
It's easier now that he's older. When he was 3 - 4 years old he would show off for attention in public.
