Why do I age white wines? For the same reason that I age reds: to let the minerality develop more fully and reveal the personality of the wine. It's possible, of course, that the wine, whether red or white, has no real personality worth getting to know aside from the cosmetic attractions added by the winemaker. In that case, the wine is probably not buying or drinking in the first place.
How long you age the wine is another matter that varies depending on the grape and its acids, tannins and phenols. Some wines take only a year or two to develop their charms while others require several decades. But as Bernie Rink, a Leelanau winemaker whose wisdom I respect, put it: "all wines improve with age." When I bought a case of his Soleil Blanc, he advised me: "It's good any time, but try to wait at least a year." That's when all of the minerals in the soil start to express themselves in the finished product. That's when it becomes wine and not just fermented grape juice.