How far do you think you could jog?

I've done a 10-mile race, reealllly slowly, a few times. When I finish, I'm always amazed at people who run marathons. Like a previous poster, for me conditioning wouldn't be the only barrier. At 55, my hips are ready to detach and my achilles tendons are playing "Dueling Banjos" after about 7 miles. Twenty-six-point-two I could not do, without borrowing someone else's body. I might be able to slog through a half-marathon without crippling myself. But I haven't.