It's 3-5 years after specialisation. So 5-6 years of medical school, internship, minimum 6 years postgraduate training for non GPs. Most people will do additional years - postgraduate degrees, repeat exams, change training programs, mat leave.
This means that people take on an obligation at 17 that comes into effect in their late 20s /early 30s. At that stage, they might have young children or be partnered with someone with a city- based job. Things that really weren't on the radar at 17.