What was Fethullah Gülen’s education and training during his youth?

During this decade (1950–60) Fethullah Gülen completed his religious education and training under various prominent scholars and Sufi masters leading to the traditional Islamic ijaza (license to teach). This education was provided almost entirely within an informal system, tacitly ignored and unsupported by the state and running parallel to its education system. At the same time, Gülen pursued and completed his secondary-level secular education through external exams.