In theory, the more fit your are, the lower the RHR will be. Though normal/average rate will depend on the individual person, some as low as 60 or as high as 99 per one minute. 72 is the mean average. In modern medicine normal can be different things to each of us, including blood pressure.
Endurance athletes might have a RHR into the lower 40's or may not. Depending on the individual again. 60 is a acceptable reading for most athletes. I have a natural rating of 60, though not in any endurance sport, that is just my normal reading.
Unless it's a genetic thing that runs in your family, a 100 RHR seems a bit high. A sudden oxygen debt when running a short 1/4 mile might be a good clue that something may need looking into. Worth the time for a checkup and serious blood work...perhaps. Good Luck.