Some 2.3 million of U.S. adults older than 65 — more than 4% — have a diagnosis of dementia. But even without a diagnosis, a certain amount of cognitive decline is normal as age sets in.

But coordinating the schedules of a bunch of adults can be a puzzle ... and-write games use simple tools—dice, a scoresheet, and a pencil—to create devilishly competitive and brain-twisting ...