Has it begun?! Mistakes and “forgetful moments” at work due to a decline in brain performance?

When I was in my 40’s and 50’s, I sometimes forgot what I was about to do as soon as I got up from my desk and even forgot how to write some “kanji characters” while taking notes. Some of my work colleagues even forget names of people they just met.
These “forgetful moments” are caused by the decrease of nerve cells in the brain and the decline in cognitive function with aging. It is said that the 40’s and 50’s is the prime age to work the brain to its fullest, but if you often repeat the same work over and over without much change in content everyday or frequently use PC’s or smartphones, only part of the brain is used.
These “forgetful moments” seem to increase and some people may wonder “is this dementia?” or they may even believe that “it can’t be helped because it’s a part of aging”. However, it is best to not leave the brain’s cognitive function decline “as-is”, because if the brain is not used, it will fade away.