Mrs. Robinson's age is left ambiguous in the books, but Ana estimates that she's in her late thirties or early forties. As food for thought, if Mrs. Robinson had been double Christian's age at the start of their "affair", that would that would make her 30 years old at the time, and her character would be 42 during the events of the series. Had she been any younger than 30 at the start of their relationship, it would make the whole "lonely desperate housewife" a little harder to believe (unless she was Linc's trophy wife or something).
This presents an interesting issue for casting Mrs. Robinson -- how old do you think the on-screen version of Mrs. Robinson should look? Would you find it believable to see a 35-year-old actress play her, or should the actress look older?
As a sidenote, while looking up information about the movie The Graduate, I found that Anne Bancroft (who played Mrs. Robinson in that movie) was 35 when she played that role. Her character was supposed to be substantially older than Dustin Hoffman's character Benjamin Braddock, who was 21. But Hoffman was 30 years old when he appeared in the movie. That's a mere five year age difference between the two actors, despite the 10+ year age gap between their characters' ages. (Sources: http://www.imdb.com/name/nm0000843/bio , http://www.imdb.com/title/tt0061722/trivia ) To me, that suggests that an actress in her mid-30's could convincingly play Mrs. Robinson in the 50S movie -- but what do you guys think? Who do you picture in the role of Mrs. Robinson?