Your Age should be your age at the time you ran the race.
The world records are taken from the AARS site: World Records as recognized by ARRS. They are as of June 2, 2017.
You can enter any number of races, including only one, and your age can differ across races.
These calculations use the 2017 age factors. The age range is 40 to 95. See 2017 Updated Age Factors.