Fact is, vaping as well as smoking, in most states is prohibited in public places.
Now, if the underage person would vape at home, that should fall under parental supervision. Same with cigarettes/alcohol/X rated movies etc. It would be up to the parent/guardian to decide, if the underaged person is allowed or make use off.
Another fact, buying vaping supplies for somebody underage, falls under the same logic and treatment in most states not all, as alcohol purchases made by adults and passed to the minor/underaged. Its illegal. Again not in all states, so check yours, damn sure its published somewhere.
My opinion, while I don't agree with most regulations, in this case it isn't wrong. Nobody should be giving cigarettes/alcohol and even eliquid containing nicotine to minors or teens under the age of 18/21(thx California grr lol) without parent permission. Even if i dont think its the same, sadly by law, its all in the same category, why so ever. However parents should keep in mind that allowing their kids to use vaping gear, needs either supervision, or a crash course of vaping saftey, as well as understanding the negative effects of nicotine in general and while starting it, might be not the best solution all around. Don't give mech mods, shitty gear or cheap/torn batteries to the underaged. That should be common sense and doesn't need a law to regulate it. Don't let your kids/teens even if 17 run over the street, promoting vaping in public places, without you being around or even aware of it, I am sure at least this could result into a ticket/fine for the person that sold/gave the equipment to the person of younger age. Doubt that the actual minor would get into trouble, because again, without an adult or person of age, they would never have gotten the gear in first place. If somebody sold it to them, well that's a whole other discussion for another day.