Some sad facts about being an actress
I don't know if this lady has a case in law, but:
(1) Your actual age DOES count in casting directors' assessment of you, and actresses in particular are rightly paranoid about hiding their actual ages. I know of an actress in her mid-thirties who looks like she is at most in her mid-twenties. She doesn't tell anyone her real age, not even her close friends. Why? She lost out on a part at the start of her career because she was 23, which the casting director deemed 'too old' to play 18. Needless to say, she wouldn't have been cast as a 23 year old because she looked far too young...
(2) There are very, very few parts in TV or film for non-name actresses over 40. As a result, many people in the industry seem to regard any actress over 40 as 'past it'; there is definitely a psychological barrier at that age. It seems entirely reasonable to assume that allowing casting directors to know an actress is over 40 would be detrimental to that actress's career, especially if her playing age was considerably younger, as she would not be seen for parts which she could realistically play.
(3) With regard to how many parts this lady has listed on IMDB each year reflecting the success of her career: films take time to make, so any credits in 2011 could reflect audition successes in 2010 or earlier; for each role she was cast in, she will have auditioned for dozens more; and if she is claiming that the revelation of her age has already damaged her career, she would know at least a year before it becomes obvious on IMDB. For instance, the number of auditions she gets called to may have drastically reduced. (Actors get called to auditions after the casting directors have seen their 'resumés', and compared them, almost inevitably, with IMDB.)
Some people have commented that $1 million is too much, but if her career has been cut short by, say, five years, that would be $200,000 a year. Quite a lot, but not impossible if she could have got a regular part in a TV series. If she looks 25 now, as some here have opined, then she could argue that her career has been cut short by 10 years, at which point $1 million looks quite reasonable.
If you are an actress, your real age is commercially sensitive information. As an industry resource IMDB should know this, even if some people who have commented on this story don't.
FYI: I work in the industry, albeit mainly in theatre rather than film, and hence understand something of the dark arts of casting. The casting director's job is demanding as bad casting can destroy a film / show. Perhaps this is why they are rather conservative about playing ages; not stating their real age is the only defence an actor has. The consequence is that all actors, male and female, are likely to lie about their age at some time or another, and up to now that has worked out fine. But, for instance, if IMDB had published her age, Gillian Anderson would probably not have been cast as Dana Sculley; she was 24 at the time, but she pretended to be older so she could be considered for the part. (Obviously, Sculley was older than 24, as she had gained a medical degree and a PhD before studying at Quantico.)