Congratulations on your purchase of this excellent fragrance.
I have had a flacon for a couple of years, that I use as a splash. It's about half used now and still smells pretty damned fine to me.
The only bad experience I've had with GV was when I foolishly bought a bottle off a guy in Singapore, off Ebay. It smelled like someone had topped GV up with Erolfa.
Keep it in optimum conditions and I reckon you'll be good for a few years. Incidentally, is it a flacon?