Pat and I are both researching Nebbiolo aeration with some intensity, and the overarching rule, the ultimate truth, is simply: THERE IS NO RULE, and do not be fooled into believing that there is. A 6-hour Audouze with a double-decant is flat-ass wrong, except, of course, for the wines that it works perfectly for. Hard to accept, but that pretty much kills the possibility of meaningful results from any vertical tasting of older Nebbiolo where all bottles are subjected to the same aeration regimen. (Sadly, that is usually a necessary pre-condition to such tastings, and why I no longer bother with them, preferring to examine each bottle in its own time and upon its own terms. Too limiting for some, I know, but the only way to draw conclusions of real value beyond “I like this wine better than that one in this moment”.) Audouzing itself is nothing more than a better-safe-than-sorry approach for old wines, not a magic bullet as some have convinced themselves. It stands to reason that delicate old wines whose aromatics and taste may be ephemeral and easily compromised are likely to lose both with the agitation of decanting. Nebbiolo most often poses the additional problem of pesky, ultra-fine sediment that may not filter out, and is best allowed to precipitate out by standing the bottle for months rather than days and left behind in the bottle during decanting to the maximum extent possible. However, the value of Audouzing ends there, and with old Nebbiolo, the absolute necessity of decanting and extended aeration usually begins.
As Pat’s work with new wines has shown, extended aeration (sometimes ANY aeration) can be an out-and-out disaster for many new-release or very young Nebbiolo, which will shut down hard with too much air, via Audouze and/or decanter. But the key is: NOT ALWAYS. It depends upon the wine. Some will never shut down and will be at least acceptably drinkable always (sans paradigm). The 2010 Castello di Neive Barbaresco Santo Stefano SEEMS to be that way, at least with food, but I am still testing. Some young Nebbiolo iwill not give one the time of day without extended aging, regardless of what one does to the wine. See the 2010 Fratelli Alessandria Barolo Monvigliero.
My work with old Nebbiolo likewise does not arrive at a fool-proof formula, but it supports strongly the opposite conclusion, that many people rarely give the wine as much aeration as it needs, at the wine’s peril. There is only one hard truth: if your bottle fades within a few hours after opening, whether with Audouzing, decanting or both, the wine is too old, flawed or both, and was never going to be worth drinking. However, there is never any harm to let even those bottles sit in a decanter to confirm the finding. On the other hand, Nebbiolo is a surprisingly durable wine that often requires many hours, and occasionally DAYS, to fully open, and it can be decanted safely with little risk of loss of flavor or aromatics. In most cases where shot bottles are not involved, old Nebbiolo will add color and the impression of greater body with extended aeration, as well as developing increasingly complex flavors and aromas. (I understand that the greater fear will always be loss of aromatics, but that loss means little if the wine remains disappointingly undrinkable. My experiments suggest that old Nebbiolo generally has a good aromatic reserve, such that one can afford to lose a little on the aroma side in order to maximize flavor, and may even develop more powerful and complex aromas with extended aeration.) I have posted extensively elsewhere on WB on this subject, so I will not repeat it here, but offer one interesting aside in passing: it seems from a recent thread here that Burgundy may also benefit from extended aeration, at least in some cases.
To the OP’s question: where is the line in the sand between young and old Nebbiolo? There is not one, and there will never be one. Pat Burton’s theory works best on new-release Nebbiolo, and the younger the better. Most age-worthy Nebbiolo will shut down within a period of months to a few years from release. There is no practical way to pinpoint the moment for any given wine. Discovering the wines that do not shut down at all is a matter of hit-and-miss experimentation and word of mouth. I would say that 5 years from release would be the likely extreme outside date for “Burtonizing” young Nebbiolo, with “the sooner the better” being the safe rule of thumb. Remember that knowledgable Nebbiolo collectors are opening young bottles only to get some sense of what the wines are likely to become in time, to understand the balance of fruit, acid and tannins, the ripeness and fineness of the tannins, the quantity, quality and ripeness of the fruit. The young bottle may be popped to inform buying decisions. Rarely is young age-worthy Nebbiolo opened for drinking pleasure by those who know what they are doing.
The notes on the recent 1999 Barolo tasting posted on WB tell me that there is danger in misapplying the Burton theory to older Barolo. In particular, the discussion on the 1999 Cascina Francia jumped out at me. The author experienced the “wall of tannin” phenomenon that Pat has described on a 15-year-old wine, and decided that it had been a mistake to aerate. False conclusion. Either the wine needed much longer aeration, or it is simply not drinkable yet, but I doubt that there was any chance of enjoying the wine or learning anything from it in the first hour or so after opening. Given how well many 1999s have been showing, to the point where I personally have come to doubt whether 1999 is a classic vintage for the ages or merely a year with a few classic, age-worthy wines, I would be surprised if the 1999 Cascina Francia did not show more with extended aeration. The only thing gravitating against that is that both the 1999 Cascina Francia and 1999 Mortfortino served up some pretty huge tannins. (My jury of one is still out on 1999, subject to more tasting. I am thinking that age 20 is the time to taste through the traditionalists and see how they are progressing. From the recent 1999 tasting, it appears thst the modernist wines are showing pretty well.)