No licensee hereunder may have more than two apprentices in training or under their direct supervision at any one time. However, the primary supervisor shall be responsible for the acts of his or her apprentices in the performance of their work in the apprenticeship program and provide the majority of the training and direct supervision received by the apprentice. Apprentices shall complete their apprenticeship in six years and shall not work longer as an apprentice unless the secretary determines, after a hearing, that the apprentice was prevented by causes beyond his or her control from completing his or her apprenticeship and becoming a licensee hereunder in six years.