Who Can Be a Supreme Court Justice?

My daughter came home from elementary school last week with notecards seeking support for her nomination to serve as a justice on the U.S. Supreme Court. I think that is it pure coincidence that her politicking coincided with the nationwide interest in potential nominees for the position following the death of Justice Antonin Scalia. But because I, like everyone else, had been thinking about how the vacancy on the court would be filled and by whom, her work got me thinking:  Who exactly can be a Supreme Court Justice? The obvious way to find the answer to this question is to Google it. I, however, started by reading the U.S. Constitution. I read it all the way through—twice (with the exception of that murky electors stuff in Article II)—thinking I’d missed something on the first go-round. All it says on the matter is that the President must “nominate, and by and with the Advice and Consent of the Senate . . . appoint . . . Judges of the supreme Court . . . .” U.S. Const. Art. II § 2. It does go on to say that federal judges “shall hold their Offices during good Behaviour . . . . .”  U.S. Const. Art. III § 2. There is nothing about citizenship (natural born or otherwise), how old a judge or justice must be, or even whether such a judge must be educated in the law. After reading this, I worried that I had missed an essential Constitutional Law class. Forget [...]