How do you feel about congress setting age limits of 70 years on congressmen or Supreme Court Justices?

After a person reaches the old age of 70, or develops a debilitating illness such as dementia or Alzheimer’s disease, should they not be required to retire voluntarily or even involuntarily. Politicians who hang on past 70 for any reason are not doing this country a service; Strom Thurman and Ted Kennedy for example?