The wiki article on wine-aging is very informative. On the first page of this thread I have tried to summarize the concept and idea behind aging wine, so do check that out along with the wiki article. In general it’s tannins and acidity, but of course there are lot of other smaller factors that come into play.
Not all wine are meant for aging, some wines are made for immediate consumption, while some wines are made specifically for long aging. The latter wine would not be very drinkable due to the big tannins or integrated flavours; these require many years before approaching; an example would be Italian Barolos.
But some people prefer younger wines vs older wines. Especially people who prefer to have more fruit in their wines would definitely prefer younger wines because they have that young fruit that older wines don’t have. Older wines ‘tend’ to have different layers of fruit and other flavours that may not appeal to someone who is just starting out or have not tried old wine before. But what people look for in older wine are the layers of textures and flavours and complexity as the fruit is shed to reveal other flavors and aromatics.
How long to age a wine is seriously guess-timation. No one can say for sure that within 10 years this bottle of Bordeaux is drinking at its peak. You’ll only know if it has hit its peak if you drink a wine that’s past its prime. For people with the money, they will buy a case or two of a wine they like and they will track the wine over several years. Let’s say they have 12 bottles, so once a year they drink a bottle to see how it develops. Unfortunately, not all of us can do that but buying 2 or 3 bottles of the same wine is an easier way to start. Typically wines will develop in a bottle and may go through a dumb phase where its aromas and flavours are muted, then it will open up again and it will reach a period where it is at its peak drinking. This is where it usually would plateau and not develop much further before declining and going past its prime. No one knows how long exactly this plateau is.
Wiki article:
http://en.wikipedia.org/wiki/Aging_of_wine