Old Vine wines are marketed in many countries with the concept that old vines produce less fruit per vine and more intense flavors. The ultimate question is what makes up a true and honest old vine? I have talked with wineries which feel 30 years and older is an old vine since they often replace lower producing parcels at the 30 year cycle. The other end of this is vineyards which have been planted and are older than 60+ years. Beyond this level are vineyards planted prior to and around the 1900's. This does not include vineyards which have been budded with bud wood from very old vines and given a marketing name.
Industry wide there is no clear definition of what "Old Vine" means. There are way to many bottlings of wine labeled old vine than there are vineyards able to produce that amount of wine. I would suggest that old vine is fruit from vines older than 65 years. Looking at these vineyards be they in Calfornia, Australia, Argentina or parts of Europe they show a unique shape and are not the trellised vines you typically see in contemporary vineyards today. These vines have avoided the plight of vine pests which kill the root systems or the leaf structure.
The best way to find honest old vine fruit is vineyard designation and case production. There are many old vine vineyards sold by: Martini, Rosenblum, Ravenswood, Catena Zapata, Starry Night, Carol Shelton and others.
A California bottling of old vine Zinfandel which produces 20,000 cases is probably not old vine in the true sense of the word. How could a wine like this sell for less than $10?? Is the blend one tenth old vine suggesting that it can use the name like a vintage solera sherry? This is a marketing tool that is being used and the consumer appears to be taking the bait.
By definition you can not over crop an old vine, it does it on its own.
How do you find true old vine wines? I have always tried to find a vineyard designated wine and look to see if they reveal their vine age. Sonoma has a wealth of old vine Zinfandel vineyards and they are highly sought after. As a consumer you should be prepared to spend in the $30+ range for real old vine wines. I personally believe that there is a difference in the depth of flavor and richness of the fruit. Perhaps getting a group of friends together and tasting a range of wines with the Old Vine label and see for yourself if it is what they advertise.