Just as you may not run as fast or jump as high as you did as a teenager, your brain's cognitive power—that is, your ability to learn, remember, and solve problems—slows down with age. You may find it harder to summon once familiar facts or divide your attention among two or more activities or sources of information. These changes affect your ability to focus, so you may find yourself getting more easily distracted than you were when you were younger.
Most people start to notice changes as they enter their 50s and 60s. Although these changes can cause consternation, most age-related memory and thinking problems don't stem from an underlying brain disease such as Alzheimer's disease. Instead, what appears to be a memory problem may simply reflect a slower processing speed and poor encoding and retrieval of new memories as a result of diminished attention. However, even though your brain may be slower to learn and recall new information, your ability to make sense of what you know and to form reasonable arguments and judgments remains intact. Hearing loss that often accompanies aging makes it more difficult to distinguish speech in a noisy environment. Because hearing then requires more concentration than usual, even mild loss of the ability to focus can affect speech comprehension.
Many of these limitations are reversible and related to poor sleep, but structural changes that take place in your brain as you age can explain some of these developments, too. Brain regions involved with memory processing, such as the hippocampus and especially the frontal lobes, undergo anatomical and neurochemical changes over time.
The result is that as you age, it takes longer to absorb, process, and remember new information. The natural loss of receptors and neurons that occurs with aging may also make it harder to concentrate. Therefore, you not only learn information more slowly, but you also may have more trouble recalling it because you didn't fully learn it in the first place. With slower processing, facts held in working memory may dissipate before you have had a chance to solve a problem.
In addition, the ability to perform tasks that involve executive function declines with age. Many people learn to compensate for these changes by relying on habit most of the time and devoting extra effort to focus on new information they are trying to learn.
Even the aches and pains of getting older can affect focus. Pain itself is distracting, and some of the medications used to treat it also can affect concentration.