How did Bruce Wayne die? Wouldn't this create a time paradox or something?

Well, Bruce Wayne died, so I have to ask this. How is it that he dies at around the age of 45 and there is a graphic novel, The Dark Knight Returns? In the Dark Knight Returns, Bruce is 50 or something. Doesn't this create a time paradox. Besides what happens to the whole Batman Beyond thing? How is he still alive in the future? Is this one of those alternate future/time line crap?