 Complete the following phrase:  As a young athlete, he was among the most promising runners of his generation, having own gold medals at the South American Youth Championships in Athletics and the South American Junior Championships in Athletics. His winning time of 1:48.53 minutes for the 800 m at the junior competition remains a championship record, as of 2016. He won silver medals at Central American and Caribbean Junior and South American Under-23 levels. Silvera competed for his country at the 