3. Gustav Magnar Witzoe, 22
Source: Adressa
Hailing from Norway, Gustav was given 47 percent of his family’s business, SalMar, in 2013. Founded in 1991, the company is one of the largest producers of farm-raised salmon. Gustav’s share brings his net worth to $1.4 billion. While he still maintains partial ownership of the company, he pursues his own interests in real estate and tech start-up investment.