Considering that only about 500K people have ever run the Boston Marathon in over 115 years, the answer is not very many.
If we're looking at just the US population, then that would be less than 0.2% of all Americans will run in the Boston Marathon.
If we're looking at worldwide population, then it would be less than 0.0001% of the world will run in the Boston Marathon.
A fellow marathoner told me that 1% of people will ever run a marathon.
Geoffrey Mutai ran the Boston marathon in 2:03. Fastest recorded time for a marathon to date.
Geoffrey Mutai of Kenya (2:03:02 in the 2011 Boston Marathon)
On April 18, 2011, Geoffrey Mutai of Kenya ran the fastest marathon ever in a time of 2 hours 3 minutes 2 seconds at the 2011 Boston Marathon.
The fastest marathon ever run is 2 hours, 3 minutes and 02 seconds - set by Kenya's Geoffrey Mutai on April 18th 2011 at the Boston Marathon.
Fastest Time: 2:03:02 Geoffrey Mutai (4/18/11 Boston Marathon)
Moses Mosop of Kenya ran 2:03:06 at the 2011 Boston Marathon
"Buster" Martin @ 101 years old
The First perso to ever run a marathon was actually a women named "Kathrine Switzer". It was in the years of 1967 in Boston
There is no time limit for completing a marathon. Sometimes people who are physically challenged in some way will take until after sunset to complete the race, just to prove to themselves that they can. The fastest time ever recorded for a marathon was just over 123 minutes at the 2011 Boston Marathon.
The fastest marathon ever was run by Geoffrey Mutai(2:03:02) at the Boston Marathon on April 18, 2011. But because the legendary Boston course does not meet IAAF layout standards, the World Record belongs to Patrick Makau(2:03:38) recorded at the Berlin Marathon on September 25, 2011.
The fastest woman to ever run a marathon is Paula Radcliffe of Great Britain (2:15:25) at London 2003. The fastest man to run a marathon is Geoffrey Mutai of Kenya (2:03:02) at Boston 2011.