Your mind works a lot like a computer. Your brain puts information it judges to be important into "files." When you remember something, you pull up a file. Memory doesn't always work perfectly. As people grow older, it may take longer to retrieve those files. Some adults joke about having a "senior moment."
It's normal to forget things once in awhile. We've all forgotten a name, where we put our keys, or if we locked the front door. Seniors who forget things more often than others their age may have mild cognitive impairment. Forgetting how to use the telephone or find your way home may be signs of a more serious problem. These include Alzheimer's disease or other types of dementia, stroke, depression, head injuries, thyroid problems, or reactions to certain medicines. If you're worried about your forgetfulness, see your doctor.
NIH: National Institute on Aging