拉美媒体：拜仁、曼联、马竞追逐厄瓜多尔17岁中场卡斯蒂略（拉媒：拜仁、曼联、马竞竞相争夺厄瓜多尔17岁中场新星卡斯蒂略）

Considering international transfer rules

I need to keep the final answer guidelines in mind, focusing on minimal formatting and asking for clarification only when necessary. Scouting players like Bayern, Man United, and Atletico in South America is common. I know Independiente del Valle is a strong prospect source. The 17-year-old would need an EU work permit, but UK rules complicate matters for minors. FIFA generally prohibits transfers under 18, with some exceptions, and there might be options for pre-contracts or monitored arrangements. I'm curious about "Castillo" and his youth connections too!