First of all we should distinguish between two types of ageing: in the barrel and in the bottle. The most important one takes place in the barrel and, contrary to what is sometimes said, doesn’t make a wine "stronger", but rather softens and smoothes it.
For this reason wines selected for ageing are originally more astringent and tannic, stronger wines able to withstand the ageing process without oxidation or spoiling.
The ageing contributes to the wines aromatic complexity, because in addition to the original flavors of the young wine, the wood used (oak or recently acacia) and the toasting the barrels go through during their manufacturing, all affect the wines aroma. So Penedès winemakers choose the characteristics of their barrels carefully, because they are an important component among the different variables that end up defining a wine.
Are there are white wines with ageing? Yes, although they are less frequent. These wines are usually fermented in the barrel to pick up the aromas and tannins of the wood, or are aged in barrel for a short time after fermentation.
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