I haven't read the book, but I remember DD was SO ready to eat before 6 months, pracxtically grabbed the food from my hands, but I didn't let her because I really wanted her to wait till 6 months. Alas, at 6months, she had no interest at all until 8 months.
However, DS is now 5months and shown no interest at all!
So I say that if your LO shows serious interest, let her go for it. My DD definitely missed her window.