In the United States, the Motion Picture Association of America (MPAA) assigns ratings to movies based on their content. Rated R movies are considered to be appropriate for adults only, and children under the age of 17 must be accompanied by a parent or guardian in order to see them.
However, some theaters may have a policy that allows seventeen year olds to purchase tickets for rated r movies for two teens, as long as the teens are accompanied by a parent or guardian. This policy is typically based on the assumption that the seventeen year old is mature enough to understand the content of the movie and make an informed decision about whether or not to see it.
It is important to note that this policy is not universal, and some theaters may not allow seventeen year olds to purchase tickets for rated r movies for two teens, regardless of whether or not they are accompanied by a parent or guardian. Therefore, it is always best to check with the theater's policy before attempting to purchase tickets.