Yes, it's sexist and discriminatory against men.
When it comes to discrimination in accommodation, the Civil Rights Act makes it illegal to discriminate on the basis of "race, color, religion, or national origin". You will notice that when it comes to accommodation, the Civll Rights Act does not prohibit discrimination on the basis of sex. Therefore, charging males more or prohibiting males is not illegal under the Civil Rights Act. It's the same reason a bar can let women drink for free but not men.