Edit: His younger self is disillusioned and no longer believes that normal humans and mutants can coexist without conflict, while older Professor X knows a world destroyed by an all-out war on mutants, so when he says, "Please...we need you to hope again," he's talking to himself in the hope of changing that future.
Here's part of an article I found on another site:
Now, as with most of the X-Men movies, X-Men: Days of Future Past will follow the comics in the larger sense, but the characters' ages, story-arcs, relationships and the overall main story differ drastically. The movie will focus on stopping the assassination of the Senator Robert Kelly to prevent the Sentinels from ruling in the future. But instead of Kitty Pryde travelling through time, Wolverine will take over the role of time travelling messenger. Patrick Stewart and Ian McKellen play the older versions of Professor Charles Xavier and Magneto while James McAvoy and Michael Fassbender play their younger counterparts, however Wolverine is played by Hugh Jackman throughout as Wolverine is practically ageless.
The movie like the comic will involve the back and forth between the present and future timelines, involving all those cast in the movie. Another major change from the comics is the involvement of mutant time traveller Bishop. Bishop though not in the original comic book story-arc, did appear in the X-Men the Animated Series version, taking over the role of Kitty Pryde, as he came from the future to warn the X-Men about the assassination.
X-Men: Days of Future Past, is a combined sequel to both X-Men: The Last Stand and X-Men: First Class. Many fans hope it will undo the damage done by the third instalment of the X-Men movie franchise, X-Men: The Last Stand. The film directed by Brett Ratner, killed off long time X-Men characters Charles Xavier, Cyclops/Scott Summers and Jean Grey.
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Singer said that Professor X's death at the hands of Jean Grey will be retconned and his presence will be explained in X-Men: Days of Future Past. Original actors James Marsden and Famke Janssen who played Cyclops and Jean Grey respectively, in the original trilogy remain absent from this film's cast. Famke Janssen being left out is not that strange as she died from the Phoenix force in the previous movie, a cosmic force that has killed her in the comics as well. However it seems although Professor X will return in X-Men: Days of Future Past his first student, Cyclops will not. Another important plot point is that of Robert Kelly, as he died in the first movie, X-Men. It remains to be seen how Bryan Singer will explain his death, if his assassination is in fact the focal point of the movie.
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