The quick answer: Do not age your Napa Valley Cabernet Sauvignon past 5 years after release.
The Reason: 95% of the Cabernets coming out of Napa are meant to be consumed within one to five years of their release.
In the US, a Cabernet Sauvignon can contain up to 25% juice from a different type of grape and still be called a "Cabernet Sauvignon". Some wine producers will blend for better flavor and some will blend for higher production yield. A popular blend in Napa is called "CMS". A CMS wine will comprise of 75% Cabernet and the other 25% will be a blend of Merlot and Syrah. Other popular blending grapes include Malbec and Petit Verdot. These grapes are meant for 'young wines', which are wines that don't age well.
There are exceptions to this rule. I consider the exceptions as 'fine' wines, and they are typically 'estate' wines that are low production and made with 100% Cabernet Sauvignon juice.
Even these wines have a shelf life of about 10yrs to 20yrs. Acidity and tannin structure are key elements to ageability and not price. So don't be fooled that an expensive wine will hold up better than a inexpensive bottle.
I recently completed a taste test between two bottles of Caymus (1997 and 2014). Caymus Cabernet Sauvignon retails for $60 to $90 a bottle. What I really love about Caymus is that it taste like the same wine, year after year. Chuck Wagner has perfected his blend and formula and you will always get dark cherry and blackberry flavor with a subtly layered of vanilla at the end.
Winemaker Notes: The 2014 growing season was another great one in Napa Valley. Our Cabernets are a blend of wines from eight of the sixteen sub-appellations.
To do a proper taste test, you should have had a chance to taste the wine before you consider cellaring it. So you will need at least two bottles. I drink Caymus every year and I have been for a very long time, so I'm well familiar with the structure and taste of their wines.
Here are my notes from this tasting:
1997: Really light in color. Almost looked like a Pinot. The viscosity (wine legs) was nil.Wine legs helps you determine alcohol levels in the wine.
2014: Dark with good legs.
1997: A little musty with little fruit smell.
2014: Dark Fruits, oak
1997: No fruits, no vanilla finish. The wine was flat and hollow of any flavor.
2014: As stated above, dark cherry and blackberry flavor with a subtly layered of vanilla at the end.
Conclusion: I wouldn't give you $10 NOW for the 1997 Caymus. However, I would have paid top dollar for it when it first came out. This 1997 Caymus was cellared and stored properly from a private collector. It just didn't hold up after 19yrs.
My advice: If you love it, drink it now or save it up to 5yrs. If you let it sit any longer you will risk not loving it anymore. Plus, you might not be around in 10 years and your relatives will end up drinking your great wine! :-)