Will I ever Run a Marathon?

I am not an athlete per ce, but now that I injured my ankle and I've been in a cast for 3 weeks, I keep thinking of how much I just want to work out. But more importantly, I keep pondering if I'll ever be able to achieve a goal of mine: to actually run a marathon. Not to win it, but to say that I actually did it. So is it silly of me, a 30 year old, to dream of such a dream or is this dream still a valid one for the new year?