What are the three types of ageism?

Ageism can happen in different forms. So we categorize them in many ways. But the three types of ageism are as follows.
1. Institutional ageism. It occurs when an institution preserves ageism in its actions and policies.
2. Interpersonal ageism. It happens in social interactions.
3. Internalized ageism. It occurs when someone accepts against beliefs and applies them to themselves.