An initiative idea has been filed with the Secretary of State of North Dakota. Signatures should start to be collected soon. It would provide that no one could run for Congress who would be as old as age 81 by the end of the term. See this story.
In 1995 the U.S. Supreme Court ruled that neither states, nor congress, can add to the constitutional qualifications for service in Congress. U.S. Term Limits v Thornton. But the vote was 5-4 and the composition of the Supreme Court has changed since 1995. Also, the North Dakota initiative provides that in case the main point of the measure is held unconstitutional, and North Dakota can’t limit the age of congressional candidates, that the ballot should show for each candidate the age he or she would be at the end of the term.