Career
Gaag competed at the first Olympic triathlon at the 2000 Summer Olympics. He took fourth place with a total time of 1:49:03.57. He competed again at the second Olympic triathlon at the 2004 Summer Olympics, dropping to twenty-fifth place with a time 1:56:28.97.
On September 6, 2008 Gaag was banned for two years beginning June 20, 2008 after testing positive for recombinant erythropoietin (EPO).