A friend of mine ran his first marathon last fall.
He set the goal of successfully finishing the race almost two years earlier. He started with 5k races. I know the first few were more walking than running, as my friend was not an experienced runner, and had been a smoker for several years.
From 5ks, he went to 10ks and then two half marathons before tackling the final goal. When I asked why he started preparing so far in advance, he said his goals were to finish, finish with what he felt was a reasonable time, and to come away without any injuries.