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