Life expectancy was shorter than by modern standards in the 18th century. Some like Washington, Jefferson, etc lived longer but they were well to do people, many of the founders were.
I don't think there should be term limits but there should be a retirement age with Ginsburg as the prime example. Breyer is getting up there too but Clarence Thomas is a pup compared to Ginsburg. Watching her doze off over the years has gotten pathetic and in most cases, you reach a point where your mind is not as sharp as it was when you were younger. Maybe an age limit of 70, 75, something like that.