Good point. However the fact is that cigarette machines are not illegal in the United States they just have to be placed in locations where persons under the age of 18 are not permitted or have easy access too.
With that being said, a vending machine of our magnitude will be unlike the vending machines you have known to sell your grand father's unfiltered and wide one hump cancer inhaler.
Machines loaded with MJ will be in a high tech machine with methods for verifying age, finger prints, eye scans, patient meds access cards and probably more. These will be nothing like the machines you remember as a younger person. Be sure of that.....
I wouldnt be surprised if it had the ability to punch you in the gut if your under age...lol. IMO ....
IMO these machines take us in to the age of the Jetsons...or close to it. Rutrow Elroy!