I read the book when DS4.5 was about 4. He falls into the 4 category. I must say though that had I read the book before he was the age of 2.5 he would not have been. The earlier milestones does not match a level 4 but the older ones do. Could be because both my kids are bilingual so the language was not AS accelerated. He did speak in 5-10 word sentences by age 2. Knew all the sounds of letters by then too. At age 2yr 7mo he started to read easy readers and about a month after that he counted to over 1000 and to 100 in his second language.
Now he is writing short stories (incredible spelling), just starting multiplication at KUMON and has incredible knowledge about geography etc.
DS29mo seems to be about a level 3 right now. He is starting to read some words in the past month. He has always had an incredible sense of humor and would tell funny jokes before the age of 2. Even before that he would express jokes just not as verbally. He is very different from his brother though in the sense that he is more imaginative, emotional, intuitive etc.
His bother was more fact based and VERY driven to learn.
I too think it is best to take the book with a grain of salt. It could give you an idea, but that's about it.
