I tell people that starting to homeschool is like having a baby…there is no "right" time. You can read all the books and think you are prepared, but you just don't know what you are in for until you take that leap and actually start.
Don't feel that you have to have "all your ducks in a row" before you start, because you will find that things change once you start. A very good friend of mine likes to remind new homeschoolers "There are no educational emergencies". You have time to figure things out as you go. The most important thing when you first start out is to get to know your child and how they learn. And you can't learn that from a book.
And the neat thing is, when you do take that plunge, you will find that homeschooling is nothing like you thought and better then you ever imagined.
P.S. One of the most common comments I hear from new homeschoolers is that they wish they had not waited so long. I have never heard anyone say that they had started too soon and wish they had put it off longer.
Also published in the 5th Homeschooling Country Fair.