if you talk about a person being of a certain age , you mean that they are no longer young but not yet old :
The show appeals to an audience of a certain age.
if you talk about a person being of a certain age , you mean that they are no longer young but not yet old :
The show appeals to an audience of a certain age.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005