Does the ballet dancer's knee hurt when she is old?

No, ballet won't hurt your knees. The only possible reason for leg injury is that many ballet schools south of the Yangtze River often require students to wear only sports socks all year round. It is cold in winter, but there is no statistics on whether they will freeze to old age and cause leg or knee pain. However, judging from the situation abroad, no matter where they are, even in countries in the Arctic Circle, their school uniforms are short skirts all year round, and they don't wear any stockings in winter, which has never been heard of when they are old. These ideas only exist in traditional China, including confinement, and only in China.