Complex sentence: Windle's first major athletic competition appearance was at 15 years of age at the 1960 Australian Championships, where his second place finish in the 1650 yd freestyle earned him a spot on the Australian swimming team at the 1960 Summer Olympics held in Rome.
Split into simpler sentences: Windle's first major athletic competition appearance was at 15 years of age at the 1960 Australian Championships. His second place finish there in the 1650 yd freestyle earned him a spot on the Australian swimming team at the 1960 Summer Olympics held in Rome.