6.12. Calculating Ages

6.12.1. Problem

You want to know how old someone is.

6.12.2. Solution

This is a date-arithmetic problem. It amounts to computing the interval between dates, but with a twist. For an age in years, it’s necessary to account for the relative placement of the start and end dates within the calendar year. For an age in months, it’s also necessary to account for the placement of the months and the days within the month.