Age Grading in MarathonView

Age Grading (or AG for short) is a method of scoring results in a way that will level the field for both older and younger runners. This description is taken from RunnersWorld article What Is Age Grading and Why Does It Matter? It is meant to be used by older runner and to let them see how a recent result can be matched against one obtained by a younger person.
For example: A marathon time of 3:15:41 of a 49 years old male, is age graded as 2:59:07.
The method for calculating the AG, is defined by World Masters Athletics (WMA). The latest version can be found here. Note that several details are needed for the calculation:

1. Race's date
2. Runner's gender
3. Runner's age

We take the last 2 items from the user's settings page.