Shaun White turned pro when he was just 13. He is now 24.
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Tiger Woods
He turned pro in snowboarding at age 13, and later did the same in skateboarding at the age of 17.
He turned pro at age 16.
There are no reports that Tiger Woods ever worked before he turned pro.
Serena Williams turned pro in 1995
Danny Way turned pro in 1989
He was born on June 16, 1951 and turned Pro on February 23, 1968, so he was 16 years, 8 months and 7 days old.
Rafael Nadal turned pro in 2001
Jack Nicklaus turned pro in late 1961.