I , do think, concerning adults---- a lot of time once a kiddos is between 6 & 11ish the ages can be hard to tell within two years. A 7 year old could look 5 or look 8....a lot depends on how quickly they are losing/gaining adult teeth, height, size, etc. So some of those ' should they be reading?!?" and similar comments vanish as people are unsure of the kids age. Under 5 and kids are easier to pinpoint ages so people are more readily aware of age in relation to vocabulary, skills, etc.
There is also the idea that kids are more independent and time spent with other kids (vs a mix of adults and kids) w/o parents after age 6/7 also plays into the amount of time parents (and stranger) have time to observe differences/comment.
I will say it depends on where you go....the nice geologist at a local museum did not blink an eye when my 6 year old wanted to talk about how diamonds were formed and/or the various rocks that are found in our state. In fact, they had a wonderful conversation and he taught her about the luminosity of some stones with a cool black light. Same with the Astronomy staff at the Planetarium, no odd comments--- but built upon the conversation she started about astroids. The Pet Store staff was thrilled to discuss dog care, name the different breeds of dogs at the groomer and the countries they were from, etc with my canine-loving kids.
Some places and locations are likely to have adults that are perfectly happy to talk to kids at whatever level they are at.
I would make and effort to have kids connect with those people to help counterbalance any unusual comments by strangers.