How to tell someone's age when all you know is her name

There are quite a lot of websites devoted to tracking the popularity of American baby names over time. (The data ultimately comes from the Social Security Administration, which records birth names dating back to 1880.) But we haven’t seen anyone ask the age of living Americans with a given name.

The method for determining the answer is quite simple1: All you really need is the SSA’s baby name database and its actuarial tables, which estimate how many people born in a given year are still alive.2

Below, for example, is a chart of Josephs. It shows how many American boys named Joseph were born in each year since 1900. And it shows how many of them are still alive today,3 assuming that Josephs die at the same rate as other American males.4