Looks like Athens Gold Medalist (and Beijing Silver Medalist) Manus Boonjumnong has finally turned pro at age 35:
http://boxrec.com/boxer/724364
Out of the 11 Gold medalists from Athens, 7 turned pro
Yan Barthelemy
Yuriorkis Gamboa
Guillermo Rigondeaux
Manus Boonjumnong
Andre Ward
Odlanier Solis
Alexander Povetkin
The 4 that remained amateur:
Aleksei Tishchenko
Mario Kindelán
Bakhtiyar Artayev
Gaydarbek Gaydarbekov