The movie is a simple concept really - an old man, a somewhat celebrated actor, at the end of his life; charming a young girl, who is the grand niece of his best friend. It can be seen as a somewhat creepy, love across the ages (Anna Nicole Smith?) but without the gold digging. But is somewhat more ... yes there is love, but it is more about the interaction between the old and the young - going to a theatre and then going out clubbing ... quoting Shakespeare and quoting Spice Girls. And even though the movie is ultimately sad, it is funny - the interactions between the old men just absolutely brilliant.
And, ultimately it is a movie about acting, by some of the most celebrated actors ever. Peter O'Toole, playing the lead old man, was nominated for his 8th Oscar (incidentally he has never won one); and it has references to other movies and plays everywhere. It is worth watching for his acting alone.