The Olympics have always done a great job at gathering the best athletes around the world to compete for gold. It's easy to not fully grasp just how great these athletes are which is why I'd love to see them throw in the average person into every competition (with the exception to those that can get people seriously hurt) and have those people compete with the worlds best.
This person would need to accept beforehand that there would be no chance for them but instead help showcase the difference. Hell, they could even be given participation medals.
I believe that the organizing committee for Paris Olympic plans a Marathon for all which is a Marathon open to the general public (so something like able to finish a Marathon in 6h) with a neat parcours like Eifel tower, Versailles castle and back.
That said, is someone able to finish a Marathon a random person or not?. Now, anyone is able to run. However, most of us would just be a danger for ourselves or the others in a judo, diving, climbing, skating event
I can answer that ! I tried to get a place for the marathon, and there were some prerequisites : to be selected, you needed to be able to run a semi-marathon.