Ageism
Ageism is discrimination against a person or group on the grounds of age. Although theoretically the word can refer to the discrimination against any age group, ageism usually comes in one of two forms: discrimination against youth, and discrimination against the elderly.
Some teenagers consider that they're victims of ageism because they are incorrectly stereotyped and generalised as a group. For instance people may think that all teenagers are equally immature, rebellious, trouble-making and so on. At the opposite extreme elderly people can also suffer from ageism in some societies. They may find they are no longer respected, that people assume they are frail and incapable, and that they can no longer make a valuable contribution to society.