At 66, Canny Chan laced up her first pair of ballet shoes, chasing a childhood dream to dance like a prima ballerina. Two years later, the Hong Kong retiree can effortlessly glide through basic routines and move gracefully to music – a proud physical feat in itself. But what most surprised her was not her improved flexibility; it was the sudden sharpness of her mind. She never imagined that the dance form would help her think and feel better, too. “Not only has my overall physical form and...