UNITED NATIONS (AP) — Dr. Felipe Paullier is quick to say he doesn't speak for the world's roughly 2 billion tweens, teens and young adults. But as the United Nations' first assistant secretary-general for youth affairs, he's tasked with advocating for young people and their concerns to be incorporated into the organization's work — a goal shared by young activists who don't always feel heard by the international community. Paullier, a pediatrician and former director general of Uruguay's National Youth Institute, started in in the job in December.