When Clay Aiken decided to step back from music over a decade ago, he did it for his now-16-year-old son Parker — and he has no regrets. Looking back on those 16 years, the American Idol alum reveals why he thinks raising a son is "happy and heartbreaking at the same time." "I'd say the most wonderful part has been watching him grow into a young man. He is an incredibly respectful and smart and responsible young man, and that is something that I'm incredibly proud of," Aiken, 46, tells PEOPLE exclusively. Now he reveals his son's secret passion: learning to be a pilot.