To introduce my younger brother, you can say "This is my younger brother" or "Meet my younger brother." If you want to give more information about him, you can say something pke "This is my younger brother, [his name]. He is [age] years old and he enjoys [his hobbies or interests]." 例如："这是我的弟弟，他叫[他的名字]。他今年[年龄]岁，喜欢[他的爱好或兴趣]"。