6 months
You must always enter the US with a passport, or a valid immigration card.
Yes. As long as the passport is still valid.
Yes, as long as you do not arrive on an airplane. You can use a U.S. Passport Card to enter Canada on foot, by car, train, boat, etc.
Yes you can, as long as your passport is valid
So long as you had a valid passport, absolutely.
Yes, it is generally fine to enter South Africa on a foreign passport, as long as you meet the entry requirements and have a valid visa if required.
An adult passport is typically valid for 10 years.
Yes, it is possible to enter a country with one passport and exit with another, as long as both passports are valid and you comply with the immigration laws of the country you are visiting.
Even Infants can enter the US with their US passport. So there is really no age limit to one who wants to enter as long as they have appropriate documents.
Yes, any visit, no matter how short or long is required to have a Passport to enter Canada, same goes for the US
You can enter your country of citizenship as long as the passport is valid- even if it has 1 day validity remaining. However, as soon as a passport expires, you cannot board the aircraft using that passport.
No, as long as you stay under a certin period of time.