Ambivalent sexism theory states that prejudice toward women comprises two interrelated ideologies. Endorsement of hostile sexism—aggressive and competitive attitudes toward women—is linked with endorsement of benevolent sexism—paternalistic and patronizing attitudes toward women. We conduct the first systematic tests of how endorsement of sexism differs across age and across time, using six waves of a nationally representative panel sample of New Zealand adults (N = 10,398). Results indicated U-shaped trajectories for men’s endorsement of hostile sexism, women’s hostile sexism, and women’s benevolent sexism across the life span. However, over time, endorsement of these sexist attitudes tended to decrease for most ages. In contrast, men’s benevolent sexism followed a positive linear trajectory across age and tended not to change over time. These results provide novel evidence of how ambivalent sexism differs across age and highlight that benevolent sexism is particularly tenacious.