Age-grading is simply a handicap system for runners over 35 years old. It levels the playing field so that performance comparisons can be made between runners of any age. A factor is assigned for each age and event length. Multiply the race time by that number and the age adjusted race time results. The age grade tables have been compiled by WAVA, the 'World Association of Veteran Athletes' (now World Masters Athletics WMA) and the tables and more info can be found at www.howardgrubb.co.uk/athletics/ (And that bit of info was taken from 'Running in the Zone', editors Steve King & Dan Cumming.) Age grade tables are compiled from world record performances in the applicable age categories i.e. the best doing their best.