Life In 19x19

It appears Fan Tingyu was the youngest: http://senseis.xmp.net/?ProfessionalRecords

And actually it appears that Fan Tingyu was not the youngest. It turns out that it's still Lee Changho, but that he's sometimes reported as having won his first international title because it's common to count age starting with 1 in Korean culture (or so I'm told...).

Lee Changho won his first world title at 16 years 6 months, definitely the youngest ever. But he was still 5-dan by that time. He became 9-dan almost 4 years later by a special promotion.

Fan Tingyu won his first world title at 16 years 7 months, and became 9-dan because of that.

Lee Changho's DOB: 1995-07-25. Won 3rd Tongyang Securities Cup on 1992-01-27 (SGF: http://www.go4go.net/go/games/sgfview/32807)

Fan Tingyu's DOB: 1996-08-06. Won 7th Ing Cup on 2013-03-06 (SGF: http://www.go4go.net/go/games/sgfview/32424)