I was looking after Oscar, my five-and-a-half-year-old grandson, for the day. We’d played football in the garden, then we’d come indoors and played three games of chess, one game of Battleships, and several memory card games. I lost the football by 25 goals to 11, all three games of chess, saw my entire fleet sunk one after the other by a succession of direct hits, and my performance in the memory card games was irrefutable confirmation of my early-onset Alzheimer’s disease.