Need competent advice, iOS version + some other things

Need competent advice, iOS version + some other things

I will describe my situation briefly and would be very grateful for some
competent advice. I've seen similar questions been closed, and hope this
is not what will happen here, and I will try to structure my question
properly.
I have recently started learning iOS development and I am half way on this
book:http://rads.stackoverflow.com/amzn/click/0321821521 which is for
iOS5.
Now, there maybe an application I will start writing in a month or so. My
first questions were: which iOS version should I target, iOS6, or iOS7?
My one concern is that I've seen that supporting both iOS6 and iOS7 maybe
a lot of work/complicated, and due to my level of experience I am not sure
if this is good thing to do??.
Shall I still go on with the book I mentioned?
I'd be grateful if someone can answer my questions.