Complex sentence: Kaye was a promising schoolboy athlete who achieved an impressive time in the 100 metres (he was faster than Theo Walcott as a 16-year-old) and he became a fan of punk rock, particularly Sid Vicious.
Split into simpler sentences: Kaye was a promising schoolboy athlete who achieved an impressive time in the 100 metres. He later became a fan of punk rock, particularly Sid Vicious.