Yes, they can still be addressed as Mr. President.
The proper salutation when addressing a letter to a former president of the United States is "Dear Mr. [Last Name]." For example, if you were writing to former President Barack Obama, you would begin with "Dear Mr. Obama." It is respectful and acknowledges their status while using a straightforward, formal address.
Yes a former US President can run for office of Vice President of the United States. A former US President can run and be elected for any other type of office.
The correct title for a former president of the United States is "former President."
Ronald Reagan
Former US President Ronald Reagan
No former US president died in 1970. Closest was Dwight Eisenhower who died Mar 28, 1969.
I address letter to former state representative as US representative.
Gerald ford
Martin Van Buren was the 8th US President.
Washington
yes
George H.W. Bush is the oldest living former US president. He is 86 years old.