Tell him that it is normal to have a good impression on the opposite sex, don't be too sensitive, and pay attention to discretion and keep a certain distance in the process of interacting with the opposite sex. It's possible that your brother met her online, and that woman is also pretty.

Trust your brother, he knows exactly what is good behavior and what is bad behavior. As long as you tell him, remember, and don't explicitly oppose them, it is really puppy love, because the child's rebellious psychology exists more or less.

If it is determined to be puppy love, of course, it is necessary to properly control this emotion. After all, he is still young. Do more ideological education