The most important things to consider, and I'm not saying anything is right or wrong, with regards to underage purchase, are these:
1. Cigarettes have been banned from underage purchase since I was a child, 40 years or more.
2. In that time there have been no actual impediments to teens who want to smoke having a steady supply of cigarettes.
3. Making it nigh on impossible for B&M vape shops to stay in business and compete with the likely proliferation of (perceived, not actual) more affordable cigalikes offerings from big tobacco will force many, if not most, people to no-choice solutions in those cigalikes.
4. Performance per puff and actual overrated performance of cigalikes will quickly lead to those who try them to want to seek other solutions.
5. If the most readily available and easiest solution remains regular tobacco cigarettes, it's not difficult to fathom that those underage will go back to what they have been perpetually doing for 4 decades, using tobacco cigarettes.
So, worrying about trying to cover every facet of availability is not only a fruitless and ludicrous endeavor, it is likely to drive kids who want to quit to continue smoking. It will force kids who want to experiment to experiment with the far more dangerous product. And lastly, the rabid pursuant of ban and restrictions and regulations perpetuates the stereotype of ignorant smokers who do not even know that information to the contrary is available.
I just spoke to a smoker this morning who was interested in my vaping. She wasn't high and mighty, she was genuinely interested. She spoke with Smoke Enders and she was told that, "electronic cigarettes are 1,000 times more deadly than tobacco". I love the information age. Links to actual scientific studies and assessments of those studies are readily available. She's getting a Nugget kit, or two. She likes my wife's Nuggets. So all of this rabid anti-vaping nonsense "for the sake of the kids" and "for the sake of public health" is, actually, the absolute worst thing that is being done to kids and to public health since big tobacco.
I am NOT saying we should just let kids vape. What I am saying is that pursuing beyond age restrictions on sales is not only fruitless, but worse, it's endangering those you are professing that you wish to protect.