NYC 上说要8.2年

https://www.cbsnews.com/news/12-reasons-not-to-get-a-phd/

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.