i agree that 75 is about right for court justices. but, i think the more important concern right now is a mandatory retirement age for the president. i frankly don't think either of these candidates should be allowed to run, at their ages. 70 sounds about right as a mandatory retirement age, meaning the functional enforcement in the primaries would be 62, to allow for two terms.

http://www.huffingtonpost.ca/david-martin/fixing-the-us-supreme-court_b_11197060.html