Depends on a number of factors, Amung them being, the amount of tannins, the PH level, Amount of SO2, and the type of closure you use.
I make all of my wine from grapes, and keep the tanins rather high since I do not bottle my wine for a minimum of 2 years. Tannins are a great preservative in wine. as a result, I do find that my Red Zins and Cab Savs have real staying power. I still have some of both wines from 1992. I open only 1 bottle a year (at crush). This year, the wine was holding quite nicely, however the ulage (the amount of empty space in the bottle) is growing. For closure, I use natural cork.
I find, however, that the flavor of most of my white wine significantly fades after 6 years (I normally do either a chardonnay or a chennin blanc). That is not to say that I would pour it down the drain, just that the wine softens to the pont of loosing the "crisp" flavor that I like in my whites.