BTW - my 'home IQ test' is this: If you kid is advanced enough that you don't want to share his highlights with your friends, chances are he's gifted. Notice that other parents are only too happy to brag away, regardless of the effect on other parents.
I would second this. It's a good litmus test.
I'd say that it also might be a good litmus test for a gifted parent and, in a round about way, that comes back to it being a good test for the child's giftedness as well. The parents who go around bragging wildly without regard or notice of others' irritation or discomfort often don't strike me as particularly astute themselves. As there seems to be some genetic basis for giftedness, I tend to assume that brilliant children are less likely to be born to parents who aren't particularly bright themselves.
Re your little guy, assuming that his reading isn't related to anything like hyperlexia, I'd feel fairly safe in going with the assumption that he is a gifted or quite likely highly gifted person. Neither of my girls read that early either but they are HG enough that just going with the GT classes starting in 4th grade that were offered by schools wasn't enough. We've homeschooled, changed schools a few times (charter, public...), grade skipped, subject accelerated, done GT pull outs, extracurriculars in their areas of extreme interest (SCUBA diving starting at age 8 for my budding marine mammologist)... I'd say that their education is almost "good enough" right now but it certainly isn't perfect and probably less so for my more 2e child who is less willing to self advocate b/c she is more concerned with fitting in and not appearing to be a braggart.
I guess that, in your situation, I would come up with some options for schools and not worry if you have to make course corrections along the way. As long as you have alternatives if something doesn't work as well as planned, you can always try something new. You have time and you don't know for sure what he'll need in a few years when he is school aged. The good news is that early elementary teachers and parents seem to be so focused on reading levels that a child who is tremendously far above grade level is likely to get noticed and that may make your advocacy job easier.
