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.

Two-player games have come a long way since checkers, backgammon, and Battleship, and today the best of them are just as complex and enthralling as any group game. We talked with experts ...