1. A PhD takes twice as long as a bachelor's degree to complete. The average student takes 8.2 years to slog through a PhD program and is 33 years old before earning that top diploma. By that age, most Americans with mere bachelor's degree are well into establishing themselves professionally.2.he average student takes 8.2 years to slog through a PhD program and is 33 years old before earning that top diploma. By that age, most Americans with mere bachelor's degree are well into establishing themselves professionally. 2.