There is no law requiring people to be age 18 to buy electronic cigarettes that contain no nicotine..
It is a matter of store policy....
In my area we have a Tobacco shop that sells cigarettes,cigars,chew and snuff and all the pipes ect. and they will sell the flavored (non-nicotine) electronic cigarettes to minors who are 16 with an ID.
The Chain parmacy in the same area sells flavored (non-nicotine) electronic cigarettes but requires people to 18 to purchase.