The need for reading glasses is a natural process of aging and happens to most people around the age of 40. The eye has a crystalline lens which flexes to help us focus on close objects. As we age, the lens loses its ability to flex and we lose our ability to focus on close objects. When you first start to lose focus on objects up close, the crystalline lens is still functional yet not at 100%. It will worsen over time and eventually plateau when a person is between the ages of 50 and 65. At this point, the lens will have lost the ability to flex at all.
A pair of reading glasses will help resolve this problem, but anyone experiencing this should always consult an eye doctor for a comprehensive evaluation.