John Cusack is convinced human intelligence peaks at the age of 12, after starring alongside pre-teen actress SHELAN O'KEEFE in new movie GRACE IS GONE. The actor was stunned by the 12-year-old's insight and maturity on the set of the film - about a father trying to cope following the death of his wife in Iraq. He says, "A friend of mine has a theory that everybody knows everything in the world at the age of 12. It's the high point. And you can see things with a clarity that you spend the rest of your life trying to rediscover. "And you can see that with Shelan."