"Getting gold is something that I have been working towards for a few years now," he said.
He said the New Zealand team played really well together in Spain to go undefeated.
"We really worked together well as a team. We combined well in the water and had numbers on the bottom of the pool at all times," he said. "It was great. It was a lot tougher competition than what I am used to."
While Shields also got to take in plenty of sights in Spain, he said the highlight was definitely taking out gold.
Shields first represented New Zealand last year during a transtasman competition and hopes to move up to the under-23 New Zealand team in years to come, with the next world youth underwater hockey championships held in two years' time.
Shields is in his last year at high school and said he wanted to become a professional diver. "Hopefully getting into the navy divers, I'm going through the process at the moment."
New Zealand also took a men's and women's under-23 team to the tournament, finishing fifth in the men's U23 grade and third in the women's U23 grade.
Shields played as a flanker for New Zealand and scored the opening goal of the tournament.