I find it weird how nobody mentions acidity and especially pH in relation to the aging capabilities of the wine (apart from one William Kelley’s post in the previous page).
Alcohol is a preservative and high alcohol on its own certainly doesn’t decrease the aging potential of a wine. If you had two otherwise identical wines, but the other one at 12% alcohol and the other one at 15% alcohol, most likely the latter one would age better because it had 3% less water and a corresponding amount more of alcohol. Port wine is a great example of alcohol’s protective qualities: it might be very low in acidity with high pH, yet they age like crazy due to their high levels of alcohol and residual sugar.
However, the alcohol in these wines - as we all know - comes from fortification. In order to accumulate higher alcohol in wines naturally, you have to get more sugar in grapes, i.e. get the more ripeness in grapes. As grapes ripen, they accumulate more sugar, but their acidity levels drop and pH soars. This is one of the key points in making wines that can last for ages: the preservative qualities of higher alcohol often do not replace fully the diminished preservative qualities of lower acidity and/or higher pH. This change always depends on the grape variety and clone; some might accumulate more sugar while keeping higher levels of acidity as they ripen, others might drop their acidity before the the sugar levels start to soar, etc.
While the aforementioned Nebbiolo is normally quite high in alcohol, it tends to keep its acidity quite high up to 14%. However, often the acidity starts to drop as the grapes have accumulated the potential alcohol of 14,5-15%, which is why it is hard to assess the aging capabilities of these high-alcohol Barolo and Barbaresco wines; we’ve have not had them in the past and the first ones have not aged long enough so that we can tell.
Grape varieties like Cabernet Sauvignon are a whole different story altogether. They come from a cool region, where they’ve normally gained 12,5-13% alcohol and high acidity. One can certainly make it go ripe up to 16% ABV, but this kind of wine most likely requires lots of intervention (acidity corrections) to keep the wine at least somewhat stable. They might be able to age to some extent due to the preservative qualities of high alcohol, but most likely aging processes happen rather rapidly due to their high pH (let alone the completely diminished protective qualities of SO2 in such a high-pH environment).
And I’ve certainly noticed that same raisiny thing Wes mentioned: wines made from raisiny grapes tend to have a raisiny taste - even though the youthful primary fruit can mask this for some while.