I would guess the average age of new members would put them as young children when they started smoking, if they smoked 15 years...
Once they quit smoking they should be able to vape 0 nic without withdrawal then, correct?
Not necessarily. Their brains will recognize the absence of nicotine, and reinforce any incorrect belief they have that nicotine is responsible for their 'dependence'. Expectancy is an amazing thing.
Here is a good example. About 20 years ago, I was the principal neuroscientist on a mostly-government scientist task force looking into the etiology of Multiple Chemical Sensitivity (i.e., when very low concentrations of various odiferous compounds [mostly organic solvent based] cause afflicted persons to experience many, sometimes very severe symptoms, presumably after some initial chemically sensitizing event or exposure]. Having observed relatively severe reactions of these people to very low concentrations of gasoline, perfume, and even scented soap, I initially drank the kool-aid and started a research program in my own lab looking at the potential for nasal epithelium receptors to directly sensitize the brain's limbic system (unlike any other sensory modality, there is a direct pathway from the smell organ to the amygdala (a nucleus of the limbic system responsible for, among other things, regulating emotional responses). Then, one day I attended a symposium that was largely attended by persons with MCS. All presenters were given instructions not to use scented soap or perfume/cologne before attending the meeting because we would be in close proximity to the MCS patients during a social event that was scheduled for after the formal program. Well, I am somewhat a creature of habit, especially at 6:00 am when I am functioning on about three hours of sleep, so I took a shower that morning using the hotel-provided soap (scented), and, without thinking, I applied a very liberal dose of my favorite cologne (which when I am wearing it, my technicians tell me they can 'smell' me coming from about 10 feet away). I went to the symposium, gave my talk, and then freely mingled with the MCS patients afterward. Not one of them reacted to my concentrated mixture of "smells". As it turned out, the MCS patients were advised that they need not worry about wearing respirators, oxygen tanks, or any other 'crutches' they used to 'survive' in the real world, because we (the presenters) were all medical professionals and would be scent free. Thus, these people had a strong expectancy that we would not be 'harmful' to them, and that we 'were on their side'. Their expectancies ameliorated their predicted responses to my "odors".
Well, to make a long story even longer, about three years later we had a final meeting of the task force and produced a document that was submitted to the Agency for Toxic Substances and Disease Registry (ATSDR) and the EPA. About a year after that, the clinical diagnosis for what had been called MCS was changed to Idiopathic Environmental Intolerance (i.e., a reaction to odors that has no definable physical cause).
The brain is a wondrous organ. It is capable of reorganizing input to meet its own specific needs. So, if it 'believes' something is the cause of an effect, it reorganizes its inputs to assure itself that it is correct. This is why I believe that nicotine dependence is "all in your head"