Age Graded % Calculation

I stumbled across an age graded % calculator on the goodrun guide website.

http://www.goodrunguide.co.uk/AgeGrading.asp

I am not sure how accurate it is but I found it very interesting.

80% is a National Class Runner
70% is a Regional Class Runner
60% is a Local Class Runner

To put this in context for me:

10k 70% 44mins   60% 50mins
1/2 Marathon 70% 1 hr 40  60% 1 hr 55
Marathon  70% 3 hr 25  60% 4 hr

This puts me in the category of Local Class Runner aiming for Regional Class Runner.