I do run into those situations all the time. My son has cousins who are anywhere from 1 to 5 year older than he is. They don't see him often, maybe once a month or so, the differences can be a bit jarring. Not jarring to the kids...jarring to my sibs and their spouses!
I'll give you a great example. We were home at my mother's house for the 4th of July and my DS and I met my sister and her 2 boys, ages 4 and 6, for lunch at Chipotle. We were enjoying the meal when suddenly DS began speaking "People we're glad to know...part five." He rambles along, reading some paragraph about a farmer, and his cousin, the 6 year old, piped up and said "What's DS talking about?" I had to explain that DS was reading the back of my drink cup.
Cousin was interested and told his mom that my DS could read! I simply, quickly said that all kids are good at different things. My nephew is learning to read in school, so I mentioned that he could read too and that he was a much faster runner than my DS is. Everyone is good at different things. Then I changed the subject.
For me, I choose not to ignore it, but also not to dwell on it. I come here when I want to talk about it in depth or chat with my DH or my mother. Otherwise, I don't downplay DS's abilities, but just to focus on his commonalities with other kids his age.
I have lots of friends here locally with kids DS's age. Some of them "know" about him, some don't, but it's not a topic I bring up. I know it will be harder to avoid talking about DS when he starts school because the differences will be up front, so for now, I'm enjoying the peace.
And you are right about the wisdom and experience of this board and the posters who are here. They are absolutely terrific!