I have good news and good news - which do you want first? Okay the good:
This is neat. Our brains are "plastic" as in malleable, and most people know this, but the extent of their plasticity is far and above what I imagined. The brain learns all the time, and re-learns way into our dottage. But not by doing the same thing over and over.
Did you ever say or hear, "I love doing crosswords, it keeps the old gray cells working." Or "I do a puzzle a day to keep my brain healthy." Well that's a myth, all a waste for the brain. If you do crosswords all the time the brain already KNOWS how to do them. It's learning nothing. And when it's not learning, making new inroads and synapses, the brain is not healthy. It will start to atrophy, get stale, become lazy. If you constantly repeat an action, the brain isn't learning.
What the human brain needs to stay healthy is (trumpets)....CHANGE. NEW THINGS. DIFFERENT ACTIONS. If you want to keep your brain working a long, long time, do things you never did before - go skydiving. Or plant a garden. Learn sign-language. Knitting. Paint something. Fly a kite, ANY thing that you haven't done before or that often. The best one? Fall in love.
The brain loves new things, it actually remembers how much it "enjoyed" learning this new thing and rewards you with better function - more memory retention, recognition, all the things we worry we'll lose in our old age. Factually, there's no organic reason our brain can't serve us well into our 90's.
So if you love someone who's elderly now, introduce them to something new as often as you can. They'll remember you alot longer for it.