The only one of these I would support is mandatory retirements ages, but only for Supreme Court Justices. Representatives and Senators are elected, so the people have an intrinsic chance to reject them for their age by simply not voting for them. Justices, though, are appointed, and to a lifetime post.
The proposed system I like the most is that a new Justice is appointed every odd-numbered year. If there is no vacancy, than the longest-serving Justice retires and their position is filled by the sitting President. That way, each Justice serves an 18-year term (at least, but not lifetime), and each President posts two seats per term.