Difficulty focusing, reaching for words, or running out of mental stamina by mid-afternoon tends to get filed under normal aging. Sometimes that is accurate. Often there are contributing factors that can be measured.
What can contribute
Thyroid function, sex hormone levels, blood sugar regulation, inflammation, nutrient status, sleep quality, and certain medications can all affect cognitive symptoms. Several of them frequently occur together.
Why sleep gets its own look
Fragmented or non-restorative sleep produces many of the same symptoms as a hormonal or metabolic problem. Sorting out which is which requires a detailed sleep history, and sometimes testing for a primary sleep disorder.
Worth investigating rather than accepting
A workup does not always find a single answer, but it frequently finds something worth addressing. Evaluation of this kind does not diagnose or treat dementia, and a history suggesting that warrants referral for the appropriate specialty testing.