My friend is 12 and the person weighs about 105 and the person is about 5.4 is the person fat if so how do they lose weigh fast?

he is not fat period im not fat and im 5.4 and weght 128 but it depends what sports does he play and whats his body fram and what pecent is fat and what percent is muscule cause im 30 percent muscule and 15 percent fat so yeh