Crossword puzzles are for old people.
I knew this to be true, because the only people I saw doing crossword puzzles were my grandparents. I can still picture my grandmother sitting in her armchair with the newspaper precisely folded, pencil in hand and brow furrowed, pausing periodically to sip her morning coffee.
My grandparents did crossword puzzles because they were supposed to. Keeps the brain active. Staves off dementia.
Where they learned this, I don’t know. But it’s a myth.
A 1999 study found “no evidence to suggest that amount of crossword puzzle experience reduces age-related decreases in fluid cognition or enhances age-related increases in crystallized cognition.” 
Puzzles don’t keep you from declining mentally as you age. Nor do they make your brain any sharper.
So what does keep your brain from declining?
Turns out there’s a group of folks in their 60s to 80s who have the brains of healthy 25-year-olds, as measured by both memory tests and MRI scans. They belong to the elite group of “superagers,” and they have something to teach us about staying young:
It takes hard work.
REALLY hard work.
Lisa Feldman Barrett, along with her colleagues from Massachusetts General Hospital, conducted the study on superagers.  Her best guess is that the key to maintaining a youthful brain is strenuous effort.
Memory games don’t cut it. If you’re having fun, you’re not working hard enough.
We’re familiar with the “use it or lose it” mantra in fitness, and we’ve always assumed it applied to the brain, too.
But fitness fanatics have another mantra: “No pain, no gain.” And that’s the mantra that will keep your brain strong.
You’ve got to suffer to make your “mental muscles” grow.
That might mean going back to school, changing careers, learning a foreign language, or mastering a new musical instrument. Do something you’re really bad at or have no clue how to do. Push yourself to the point where you’re tired, frustrated, and ready to give up. Work it ‘til it hurts.
Then, once you’ve mastered one thing, switch to another. You have to keep challenging your brain in new ways. You can’t get complacent.
No wonder crossword puzzles don’t work. Doing a puzzle every day is like doing the same workout over and over again. Perhaps it helped you gain fitness in the beginning, but now it’s just routine. You need to shake up your workouts, both physically and mentally.
Interestingly enough, you don’t have to perform mental gymnastics to keep your brain strong. Actual gymnastics works just as well.
Physical effort works out the brain as well as the body. So sign up for a triathlon, take up Bikram yoga, or start lifting weights. Get huffing and puffing. Feel the burn.
From this perspective, it’s no wonder retirement signals the beginning of the end for so many previously fit seniors. Easing into a comfortable life of relaxation and ease may be the last thing you want to do at this stage in your life.
A better use of retirement might be to start a small business, travel the world, or get a new degree. Anything that pushes you mentally and physically.
The final component of a superaging brain is diet. You won’t have the stamina to keep up unless you nourish your brain with the nutrients it needs.
Dr. Oz’s “brain diet” is a variation on the anti-inflammatory diet, with superfoods including elderberries, pecans, chicken giblets, homemade vegetable juice, and beets. The more fruits and vegetables you can pack into your diet—with as few processed foods, animal fats, and sources of sugar as possible—the better.
Will physical and mental exercise, along with a healthy diet, prevent dementia?
Unfortunately, the jury is still out. Healthy habits reduce your risk of dementia but don’t prevent it entirely.
Still, there are worse goals than sailing into old age with the brain of a 25-year-old. Makes it easier to finish those crossword puzzles.