Boys and girls (at least the majority of them) behave and socialize visibly differently, and can benefit from it. Races do not have the same sorts of inherent distinct needs, and if they do it's typically more granular than "white" or "black"; more likely you want time with the Italian side of your family, or the Somali side, or with your girlfriend's Panjabi roots.
Why do you think so many women occasion a "girls' night out", or men "hang out with the guys"?
Boys and girls have a lot more significant physiological and sociological differences than whites and blacks. Whereas, for example, the noticeable differences between a Japanese woman and a Mestizo woman come down to things like whether the earwax is likely dry or oily, or the probable size of teeth or lips. These sorts of things have basically no relevance or importance to social relationships.
Drawing meaningful distinction between the cohort characteristics of boys and girls is not sexist. I have no interest in determining the rights or freedoms of either group based on these characteristics. I would merely suggest that people in either cohort are likely to have needs that differ more than within each cohort. A hen and a rooster are both chickens, but they are meaningfully distinct as well.