Average Age Grading Calculator (10k, 10 mile, half marathon)
This calculator uses fractions of ages eg 52.5 when calculating age grade.  This means it uses interpolated world record times.  eg if the 10k world record time for a 52 year old is 30 minutes, and for a 53 year old is 30 minutes 30 seconds, and you are 52.5 years old, it will use 30 minutes 15 seconds to calculate grading.