Possible Clues:

• For mature audiences, say
• Racy, say
• Like 'The Exorcist' and 'Lethal Weapon'
• Like slasher films, typically
• Not for children, as a movie
• Not for young eyes
• Like "Stand By Me," even though its main characters are all kids
• Deemed not suitable for kids
• Containing some sex, say
• Like 'The Godfather'