The age distribution of a population is a product of a century of demographic history. This paper describes how the history of births, deaths, and migrations has fashioned the US age distribution in 2018. It also shows how that history, combined with contemporary processes, was actively producing changes in the age distribution between 2013 and 2018. Changes in survivorship, migration, and births all contributed to population aging during this period, with a declining growth rate of births the leading contributor. Using a novel approach, the paper demonstrates how the inertia reflected in changing age distributions sheds light on the future population of the United States. Massive growth in the population above age 70 will occur by 2033 if recent age patterns of age-specific mortality and migration are maintained.

中文翻译：

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美国不断变化的年龄分布

一个人口的年龄分布是一个世纪人口历史的产物。本文描述了出生、死亡和移民的历史如何影响 2018 年美国的年龄分布。它还展示了这段历史与当代过程相结合，如何在 2013 年至 2018 年之间积极地产生年龄分布的变化。在这一时期，人口老龄化、人口迁移和出生都是造成人口老龄化的主要因素，其中出生人口增长率下降是主要原因。该论文使用一种新颖的方法展示了年龄分布变化所反映的惯性如何揭示美国未来的人口。如果保持最近年龄别死亡率和迁移的年龄模式，到 2033 年 70 岁以上人口将出现大规模增长。