While there are extensive rules relating to when and where minors of various ages may sell alcohol, there do not appear to be any such rules in Arizona regarding tobacco.
Statute A.R.S. 13-3622 forbids selling/providing to a minor, which would probably discourage any business person from employing a minor where tobacco is sold, as he/she may be considered to be "having in his possession" or "accepting" or "receiving" tobacco.
This is a fairly far-reaching statute, and this area of law is not as clear as it might be, but a minor should probably stay away from the sale of tobacco.