
Character mistake: When McCall put his gun to his head and pulled the trigger, he's saddened that it didn't go off. Most handguns (including the one he was using), after the last round is fired, the slide locks to the rear. He would not have made the mistake of thinking it was loaded.
Answer: Sophie finds Donna's diary from 1979, being the year Sophie was conceived meaning she was born in 1980 (as the diary entries are from July/August). So the movie is set in 2000.