That is a question only you can answer. While the chances appear small, it is small for anyone to be a world class runner. But should that stop you from trying? The marathon has more older runners than the other faster events. I say if you really want to put the time and effort to see how good you can be, and you have the time to put the appropriate training in , go for it. If later it looks like you can't become world class, at least you know you tried and in the process you probably became super fit. If this is just a passing phase, after a few real work outs you'll know pretty quickly. Don't let anyone determine what your dreams should be. God will direct your path if that's what you're suppose to be doing.