I'm a big fan of Marathons. I love to run them! They are just over 26 miles and are exhilarating. 
I commend you for your dedication.  How long do you have to train for a marathon?
It usually takes me some time to train, but on top of it being an aerobic activity it's also something that requires a lot of mental strength and stamina.
I can imagine.  When did people start running marathons?
Well, it was one of the original Olympic events in 1896, so they have been around for quite a long time. The distance didn't become standardized until 1921.
I wonder why they settled on 26 miles?  Is there any significance to that number?
I'm not really sure, but maybe it has something to do with the distance it commemorates. It is said to commemorate the run of a Greek soldier named Pheidippides who was a messenger from the Battle of Marathon to Athens. He reported the victory.