What are the causes of precocious puberty in boys?

Multiple: Testicular tumors, central problems that stimulate the brain to start signals to the testicle such as tumors, head trauma and other rare syndromes. The most common cause is idiopathic meaning no known cause.

Puberty : Boys are more likely to have pathological conditions causing true puberty. These include brain tumors or lesions. The vast majority is idiopathic ie we don't know.