hi Tata83~ my son is also 4.5 years old ... i bought books with more pictures and less words. we read them before bedtimes.. and during the day, my son and daughter will take out the books to flip through. Not exactly reading since they are still too little.
i think you can also encourage him to read book (or tell stories he knows) to you~ so, instead of always read by you, he can participate more in reading. My son sometimes will act like us and read storybook to his little sister (even he doesn't know the words, but he remember the story.. and then by looking at the pictures.. he guess which part of the story belongs to ..)