age limit       
noun [ C ] uk/ˈeɪdʒ ˌlɪm.ɪt/ us/ˈeɪdʒ ˌlɪm.ɪt/
 年龄限制
the age at which a person is allowed or not allowed to do something
  the upper age limit 年龄上限 
 The lower age limit for buying cigarettes in the UK is 16. 在英国,允许买烟的最低年龄是16岁。