Ageism is perhaps the most paradoxical prejudice: we are, barring accident, discriminating against ourselves. Members of the persecuting in-group are through the course of their lives gently conveyor-belted into the persecuted out-group, which is, when you think about it, a very strange state of affairs. If the rich inevitably became poor at a certain life stage, you might expect society to fill with vigorous socialists. But ageism persists. Why? The best explanation perhaps is that it comes down to a sort of mass delusion on the part of the young. John Steinbeck wrote of America’s “temporarily embarrassed millionaires”, the poor...