Well, if it was a daughter who wanted to wear boy's clothes, it basically wouldn't mean anything.
Clothes are just fabric and don't have a gender.
Men's, and boy's, clothes are also dull uniformed compared to women's.
Boys get raised to suppress their girly, and feminine, sides. For instance, girls can usually have long or short hair, but boys only short hair. Meantime, the male gender also requires rights, gender equality, liberation. The biggest obstacle to that would be ironically other males.
If a man, or boy, does anything not considered the norm for men, his sexuality must immediately be brought into it. That is so immature. Some people need to wake up and grow up.
I know also of a good facebook group about that, if interested.