Should Supreme Court justices have their terms limited?

[Bo]

Also, if yes, how many years maximum should each justice be allowed to serve.

I'd say Yes, and each SC Justice should be able to serve a maximum of 15 years.

[Bo]

Imagine if their terms were all limited at the same time - and the President still had the power to appoint them.

That should be avoided. Also, if their terms were limited, Justices could still retire (or die) before their terms are up. Keep in mind that the Founding Fathers did not intend for most Justices to stay on the Court for 25-40 years. Due to the lack of modern medicine in the 18th century, the Founding Fathers excepted most Justices to die way before they served that long. However, due to modern medicine, many SC Justices can stay on the Court much longer than the Founding Fathers envisioned they would. I believe Canada and some other countries have limits on how many years (and/or until what age) a Supreme Court Justice is allowed to serve.