The subconscious has billions of things being managed...ALL THE TIME. Now, there are certain cases of this, but like everyone else here - you do sound like a generally normal 46 year old.
Kaiden is right. It is a self limiting belief. You actually have more potential that you've ever dreamed possible. Breaking old habits is not as difficult as you may believe. Many of us are used to having change happen gradually and over time, but believe it or not - change happens INSTANTLY whether you realize it or not.
Speaking on more proof based terms, haven't you ever had a time in your life when something happened inside you that totally altered many of your perceptions on something? Like a revelation, or some mysterious dawning on you like you had found something that had been missing the entire time, but never knew that you were even looking for it?
Changing behaviors and habits is the same way. It can be done effortlessly and even instantly many times. With breaking old reading habits, the best thing to do is to intentionally practice using the system everytime you sit down with something to read. It's that simple.
Try doing nothing but the PR Whole Mind System on reading material for several weeks, and then just try going back to normal reading habits for 3-4 days. You'll notice it's harder, and feels weird. It is said that the first rule of behavorial psychology is "whatever you reinforce, you will get more of."
I, myself, DID learn with the book, and the book only. Yes, it can be done. Yes - you can be successful with JUST the book.
Be warned however - they say that it's harder and takes longer to learn, but when I look back upon it, I don't see that as the case. 
It is true that at the age of 46, you're no longer building and developing new neurons, and thus are not quite so capable of easily learning. Remember when you were a child? Not a care in the world? Not a clue about anything? It was your developing brain and playful curiousity that allowed you to learn life's core academic basic skills so easily. Addition, multiplication, ABC's, your sentance structure and writing style, etc.
Then again, maybe you might make a list about many things you have been successful in learning recently, and realize, "Wow, I had the same basic mindset and attitude as I did when I was a child. This is so interesting, I've GOT to know about it!"
Now imagine PhotoReading. Obviously, you've already found something that's compelling and sparked with intrigue about the system. Can you see yourself one day getting so good with the system that you can take in entire books, containing at least 70% comprehension after spending only 15 minutes on it? It CAN be done! 
When your mind wanders, of course it's okay if it's during the PhotoReading step. In fact, the more the merrier! One of the entire points of the PR step is to get your conscious mind out of the way and let your subconscious get at the information that you're needing to take into your long term memory.
SuperReading and Dipping is extremely easy. All you have to do is take your eyes down the center of each page, your purpose in mind, and simply read whatever text attracts you. Remember to try and come up with a clear purpose before using PRWMS on any book. The purpose needs to explain what you want out of it.
Good luck,
youngprer
