Las Vegas massacre victim Quinton Joe Robbins, just 20 years old, “was truly an amazing person,” his grief-stricken family said.Robbins, who was killed in Sunday night’s mass shooting at the Route 91 Harvest festival, was a lead recreation assistant for his hometown of Henderson, Nev., just outside of Vegas.City spokeswoman Kathleen Richards said Robbins worked part time in the Parks and Recreation Department’s sports division, coordinating activities.