He's proof you don't have to milk cows to have a career in New Zealand's multi-billion dollar dairy sector.
"The opportunities in the agri-food sector are endless, even if you live in the city. You just have to be passionate," he said.
Robertson was one of seven contestants from across the country who competed in this year's grand final.
The victory was the culmination of days of gruelling practical and technical challenges which tested their skills, knowledge and stamina.
Competitors had to drive a large grape harvester, make sausages, assess health and safety risks using a virtual reality simulator, install an irrigation system for fruit trees, market a line of sheep and sit an agri-business exam.
James won a prize package worth at least $75,000, which includes a trip to Ireland.
He also took out the FMG People's Choice Award, winning $1,000 for his Auckland Young Farmers club.
Despite his young age, Robertson has had a long involvement with NZ Young Farmers which started during high school.
In 2013, Robertson and a fellow team mate from Hamilton Boys' High School won the TeenAg Grand Final.
It means the Massey University graduate is the only person to take out both grand finals.