As you said, after the formation of Earth, it took only a few hundred milion years for life to develop. That is incredibly short, almost instanteneously as soon as conditions for life were met, life formed. Our galaxy, the Milky Way, formed almost as soon as galaxies could form. So here we have a situation where a inteligent civilization could have formed anywhere in our galaxy 13 bil years ago or at any point in time after that. Chance is, if they had, by now they would have conquered the whole galaxy. Absence of any sign of inteligent life can be wxplained by the Great Filter. It could be any of the following: 1) interstellar travel is never feasible for any civ, no matter how advanced, 2) Earth-like planets are so rare, that we are probably the only inteligent civ in our galaxy, 3) Earth-like planets are not that rare, but inteligent civs tend to destroy themselves before they manage to spread out to other planets... We don't know what the Great Filter is, but it must be pretty destructive for a civ. I just want to point out the fact that the Great Filter is probably still ahead of us and that we shouldn't take our existence for granted. We need to meticulously examine and neutralize any possible threats to human civilization. This is not fearmongering. It's just common sense, after you take all the facts into account that I laid out.