Question: At what age do you start high school?
Disambiguated questions and answers: question: At what age do the youngest students typically enter 9th grade in US high schools?
At what age do the oldest students typically enter 9th grade in US high schools?
At what age do the youngest students typically start high school in Canada?
answer: 13
14
15
Natural Questions answer: 14 -- 15 (from the Wikipedia article "Education in the United States")