There are websites for mental stimulation, google it.

Johns Hopkins has a White Paper (about $20 for their PDF file) that addresses these issues. They have several papers you can get for free, as well as updates.

I would suggest you find an area you are passionate about. Passion seems to help my internal "search engine" find words. Anger and Adrenalin work too (short term of course).

Go to the Mayo Clinic and type in "MCI". Mild Cognitive Impairment is an interesting area. I detoxed off morphine (car wreck - I am 100% disabled) due to Respiratory shutdown in 2008. My mind does not function as well as it did. Not sure why. Not a function of age, more a function of opiates and other prescribed drugs. I also did public speaking and taught graduate level courses. I would not be able to do that today. BTW, I am 64. Most of what they printed about MCI fits me. I have been retired since age 55 (car wreck was 9 years ago).

Good luck with your search, at least you are intelligent enough to understand things aren't functioning as well as they used to.