He's Cuban. He'll need to defect from Cuba to become a pro. It's better to do it with a gold medal than without it.
Also, it's not true that there are lots of teenagers who get medals. On the last Olympics there was exactly one teenager who got the medal, Cuban Robeisy Ramirez who is still an amateur anyway. Other guys were comfortably in their 20s. Maybe it used to be like this in the past where you had American boxing prodigies winning at young age, but the amateur competition looks tougher right now.
It's only amateur in name anyway, it's a full time job for many.