For Congress, House members should be limited to four 2-year terms (8 years max), and Senate members limited to two six year terms (12 years max), with a possible extention of ONE additional term for members in leadership positions (Speaker, Whip, etc.) in order to have someone experienced in those positions. Members of the house must be at least 25 but no older than 75. Members of the Senate must be at least 30 but no older than 80.
Members of the U.S. Supreme Court should be limited to three 10-year terms (30 years) or until age 75, whichever comes first. Voters should have the option to dump them every 10 years.
I throughly disagree that we the idea that we can "term limit them ourselves" at the ballot box. Most members of Congress are in "safe" gerrymandered districts designed to elect them for life, regardless of how poor a job they do. That's how Barney Frank can get caught running a male prostitution ring in his house and still manage to get re-elected easily.
All of which would require Constitutional amendments, and which will never pass. Limiting Congressional terms would end up a situation where staffers would be running both bodies (especially if those were lifetime limits — otherwise members would just rotate back and forth between both bodies, what they’re already doing in some state legislatures).