Van der Have said Triumph Studios has made "great progress" on the game, but will need "a bit more time" to create all the game's features and content.
"Age of Wonders III is the largest game in the series and with the additional polish we hope we can give you an even better experience," he said.
Age of Wonders III was previously targeted to launch during fall 2013.
Van der Have explained that Triumph is planning a "great" preorder promotion and will show off the game to media during Gamescom next month.
Age of Wonders III is a strategy game that casts players as the leader of a fantasy realm. Gamers can play avatars similar to Lord of the Rings characters Sauron and Galadriel, or Lord Stark from Game of Thrones. The game is fully 3D and runs on the third iteration of Triumph's Creator engine, itself an evolution of the technology behind the Overlord games.
Minecraft creator Markus "Notch" Persson is co-funding Age of Wonders III, though Triumph said he is "pretty much hands-off."
"We are working our asses off so we don't disappoint him and our other fans," the company said.