Question: Who has been the youngest president of usa?
Disambiguated questions and answers: question: Who has been the youngest president to be succeeded to the office of usa?
Who has been the youngest president to be elected of usa?
answer: Theodore Roosevelt Jr.
Theodore Roosevelt
John F. Kennedy
Jack
John Fitzgerald Kennedy
"John-John"
JFK
Natural Questions answer: Theodore Roosevelt (from the Wikipedia article "List of presidents of the United States by age")