This depends on some factors. A young man who enters College seminary immediately or shortly after High school will spend the traditional four years there, getting a sound foundation in philosophy and the other liberal arts, then move on to the theological seminary for four more years of specialized study in Scripture, Theology, Church History, and related fields. He would spend a total of eight years in the seminary after high school, comparable to another young man who goes to law school or gets an MBA. or goes to medical school.
Some men begin their preparations for the priesthood after already obtaining a college degree. Usually, they need a substantial amount of philosophy and preliminary level theology before moving on to graduate level theology. Therefore, they enter a one-year or more often two-year program called Pre-theology. Once prepared in this way they enter the usual four-year theologate. They spend a total of five or six years in the seminary.