@iamsuperandrew ’attending’ and interaction has been directly said to be a factor in becoming a StoneWaller. That is, not just buying wine, but going to the winery for lunch, cellar door etc.
Also, there isn’t necessarily a particular hurdle to be cleared. A couple of years ago, a number of people became SWers much earlier than expected. At the winery they told us that the original crop of SWers were ‘getting on’ and buying less wine, so they had more stock available, so able to bring more into the fold. I wasn’t one of the first crop, but pretty early and am certainly buying a lot less than I used to.
So timing comes into it.