This article is from the WineMaking FAQ, by malak@CAM.ORG (Don Buchan) with numerous contributions by others.
There are varying opinions on the exact effect of bulk aging on wine;
some wines benefit more than others. It is generally agreed that it is
a good thing.
Some references will say that a wine ages faster in bulk while others
in the bottle. Bottom line is that wines will age differently in the
bottle than in the carboy, and each adds a different aspect.
Bulk aging is not recommended in plastic carboys beyond three to five
months as the plastic is sufficiently porous to allow oxidation.
Using oak barrels is covered above.