It might sound horribly ageist, but I’m inclined to agree. Representing the interests of millions upon millions of people is an incredibly taxing and demanding job, which nobody in their 80s should still be doing; especially not without some sort of fitness test.
Term limits are absolutely needed, along with age limits on how old you can be while in office. Using 65 as an example, if you'll turn 65 while in office, too bad, you're intelligible to run.
Term limits have been put in place in several cities and states too I believe, and they've resulted in more corruption and lower quality governance. It's the worst possible outcome.
Think about the type of person who could afford to run for Congress for a few terms. They're probably retired and/or wealthy. This just entrenches them in power even more. And it seems there is a skillset that politicians pick up over their tenure.