Population ageing is a major demographic challenge for humanity. Since population structures evolve slowly and predictably, the demographic, economic, environmental, and social problems of ageing have been anticipated and discussed for many decades.¹ Yet the focus of these discussions has always been the elderly population, with elderly people often defined as those older than a threshold—eg, 65 years or age at retirement—or with a certain number of estimated remaining years of life.² Such a focus is quite reasonable and understandable but not entirely correct.

中文翻译：

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区域人口结构一览

人口老龄化是人类面临的主要人口挑战。由于人口结构的变化缓慢且可预测，因此数十年来人们一直在预测和讨论老龄化的人口，经济，环境和社会问题。¹然而，这些讨论的重点始终是老年人口，通常将老年人定义为年龄超过阈值（例如65岁或退休年龄）或有一定估计剩余寿命的老年人。²这样的重点是相当合理和可以理解的，但并不完全正确。