As people age, their bodily systems — including the brain — gradually decline. “Slips of the mind” are associated with getting older.  The brain controls many aspects of thinking — remembering, planning and organizing, making decisions, and much more. These cognitive abilities affect how well we do everyday tasks and whether we can live independently. 
Due to the gradual decline, some of these functions are impaired.
STRUCTURAL CHANGES IN THE BRAIN
The presenting changes as a result of the decline reflect changes in the brain structure and chemistry. The overall volume of the brain begins to shrink when we’re in our 30s or 40s, with the rate of shrinkage increasing around age 60. But, the volume loss isn’t uniform throughout the brain — some areas shrink more, and faster than other areas. The prefrontal cortex, cerebellum, and hippocampus show the biggest losses, which worsen in advanced age.
Our cerebral cortex, the wrinkled outer layer of the brain containing neuron cell bodies, also thins as we age. Cortical thinning follows a pattern similar to volume loss and is especially pronounced in the frontal lobes and parts of the temporal lobes.
The number of connections, or synapses, between brain cells also drops, which can affect learning and memory.
As an individual ages into late adulthood, psychological and cognitive changes can sometimes occur. A general decline in memory is very common, due to the decrease in speed of encoding, storage, and retrieval of information. This can cause problems with short-term memory retention and with the ability to learn new information. In most cases, this absent-mindedness should be considered a natural part of growing older rather than a psychological or neurological disorder. 
Older adults often become anxious about memory slips due to the link between impaired memory and Alzheimer’s disease. However, Alzheimer’s and other dementias are not a part of the normal aging process. 
Common memory changes that are associated with normal aging include:
● Difficulty learning something new: Committing new information to memory can take longer.
● Multitasking: Slowed processing can make planning parallel tasks more difficult.
● Recalling names and numbers: Strategic memory, which helps with remembering names and numbers, begins to decline at age 20.
● Remembering appointments: Without cues to recall the information, the brain may put appointments into “storage” and not access them unless something jogs the person’s memory.
AGE RELATED BRAIN DISEASES