Ah well, you never know what you are capable of, until you try. I couldn't have imagined doing this 3 years ago. Now?... I'm already looking for bigger (and longer) adventures in the future!
I spotted that as well, there were other people that didn't feature in the lists... but in a total of 33 people who started the race there were just 5 under the age of 40 (one was 26, one was 27, one was 35, and then two were 38 including me). The rest were all over 40.
I suspect that is the nature of the event. Choosing to run 20-40 miles is a big undertaking for many, and only really appeals to a small number of people who wish to push and test their limits. Endurance sports are events which experience and maturity is key... the ability to manage your body and pace yourself effectively takes patience and practice.
It's probably also because running back and forth along a 3 mile stretch of path for 7 hours is not that exciting for the youth of today!