There is no magic divide separating the motivational interests of a teenager from an 18-22 year old.  Teenagers aspire to be young adults, so there is an inherent crossover effect in advertising directed to this segment of the population. 

Teenage males can be influenced by advertisements associating smoking with sexual attraction in the same manner as a young adult male.  Messages of establishing independence from authority and projecting a virile masculine image can have a general appeal to the males of this age.  Similarly, associating cigarette smoking with a slender, independent, successful woman has a positive appeal to both teenage girls and young women.

For the tobacco industry, recruiting smokers is the most effective strategy for the spread of cigarette smoking.    Allowing tobacco advertising targeted towards young adults will guarantee that an effective pro-smoking message will reach our teenagers