Here's an interesting web site that attempts to compute a handicap time for heavier runners.

http://academic.udayton.edu/PaulVanderburgh/weight_age_grading_calculator.htm

There are dozens of age grading calculators on the net but this is one that tries to work in an equivalence for weight. I plugged in my latest 5K, 27:29 which doesn't sound too impressive on the surface, but when I include age 61 and wt 202 lbs, it gives me a 19:53. File it under "in your dreams", but it's a fun exercise.

Try this one for plain age grading, excluding any consideration of weight, based on the world record for each age. It brings you down to earth a bit but still a very good tool to see where you sit in the global scheme of things.

http://www.heartbreakhill.org/age_graded.htm