I found more information on the Highlander game over at IGN.com. It looks like my guess was right, Owen is going to be around 2000 years old. Smart idea on the game makers, it gives them a lot more history to explore in the game.

Game Premise (obtained from IGN.com)

Owen MacLeod, born in Gaul over 2000 years ago, was the son of a tribal chieftain whose village was crushed by the Roman Empire. MacLeod was sent in chains to the gladiatorial arena in Pompeii where he faced what he imagined to be a short life of battle. However, it was in the Coliseum where he was killed, only to miraculously recover and begin a new life as an Immortal. Fighting through centuries against other Immortals in legendary battles ending in death by beheading, MacLeod now faces a mysterious and almost all-powerful Immortal who is hunting him down in New York City. With his mentor, Methos, guiding him, MacLeod learns that the only way to destroy this ultimate nemesis, is to search out the three fragments of a mysterious stone that when pieced together, yields unlimited power to the Immortal who possesses it.

Highlander: The Game enables gamers to exploit the powers of immortality and manipulate situations that death would normally prevent in order to combat the forces of evil. MacLeod can use his body as a conduit for electricity or fire, impale himself with enemy weapons to disarm them, and survive long falls from buildings to escape enemy attacks. Gamers can also master a variety of Highlander swords including the Claymore, Katana, and Twin Gladius.