There is no obligation... and no limit in time ! In average, our mentors will accompany 3 youngsters during their mandate. However, it's important to keep in mind that once you start a duo you will only accompany one mentee in the 6-month to come.
Why ? The purpose of this rule is to allow you to concentrate on a single young person and dedicate a few hours a week to him or her, without overwhelming yourself with work.