Medical exams are required, especially for seniors, even if the visit is less than 6 months. My parents applied visa there this month and they were also asked for medical exams. It wouldn't take very long as they got visa today, but the exams are more expensive than here - RMB1500 each. Medical results should have effects, otherwise what is the ground for such request.
Your parents have to make an appointment with any designated doctors before they go to Shanghai. There is one in the same building of the Canadian Consulate General in Shanghai. A list of all designated doctors should have been sent to your parents with medical forms. It took two weeks for my parents to get their visa after medical exams.