BB:
I love that you started a journal talk about being a head of the time (age wise with your child) so when you do have him tested or the school you will be able to provide a lot of useful information. Or even more important keep documentation to share with him later on in his life. Here is the funny thing as I read your argument on not very strong in reading. FYI: it is not typical for 18 mth olds to know all their ABCs upper and lower and to be able to read a few words by 2. I think you saw his interests in math and got excited by it, which who wouldn't but from what you decribed your son was pretty equal in verbal and math.
So now with this equality ... is it normal? not for the ND child.
As for my story it is still short because my DD is only 29 mths but she has been able to count up to 10 (rote and count)before 1 yr and up to 20 solidly now. When she is interest she will go beyond 20 but that is only when she is interested. She also is able to add and subtract but again only when she is interest. Like today it evolved around playdo and how many seahorses mommy was making her. That was adding as she continued to demand and later when picking so many up in her hands and squishing them together came subtracting. So that is for the most part math and I would say she is weaker in the math side than her verbal. She has always been that verbal kid that collected words and used them in long sentences with proper grammar. Even at 8 mths she was able to replace I with you. And her verbal tenses are usually about 90 to 95% accurate. On occasion she will say a present tense when it should be past. She also has this knack for being able to say any word no matter how complicated and usually on the first try. The word of yesterday since she was driving me nuts was mischievous. She got it on her first try. She also had her ABCs upper and lower and the sounds each letter makes by 18 mths and was reading some memorized words by the time she was 2. So please someone correct me if I am wrong with my assumptions but this is not normal such as BB's son is not.