Arnold Schwarzenegger

Before he was thirty, he already served in the army and won numerous body building competitions, while simultaneously going to business school and working at a health club. Once he immigrated to America, he continued to compete in bodybuilding competitions while also starting a bricklaying business, which he then used the profits from to start a mail-order business selling fitness related products like workout instructional materials. He then used the profits from that and his winnings in body building competitions to start a real estate investing business, ultimately making him a millionaire in his 20s, long before his breakthrough role at the age of 35 in the 1982 Conan the Barbarian.