Complex sentence: Ye started swimming at the age of 6 after her kindergarten teacher noticed she had large hands and feet, who after five years of training, became a versatile swimmer competent in all four major swimming strokes.
Split into simpler sentences: Ye started swimming at the age of 6 after her kindergarten teacher noticed she had large hands and feet. Within five years of training she became a versatile swimmer competent in all four major swimming strokes.