Because of their elasticity, the lenses in our eyes can change the refractive power of light by contracting or expanding. This process is called accommodation and is necessary to see things sharply at different distances. This is the only reason why we can, for example, focus from the speedometer in our car to the next street sign - and see both sharply. Accommodation is not even perceptible to us, because our eyes change focus in a fraction of a second.
Due to age, the lenses of the eye lose elasticity, which means that focusing becomes more difficult as the years go by. This is why many people from about 45 years of age onwards find it increasingly difficult to see objects that are close - they become blurred. Numbers and letters become blurred and reading becomes increasingly difficult.
Involuntarily, you start holding the newspaper or book further away. This works quite well at first, but the arms are not infinitely long. At some point, even they can't help any more.