O'Sullivan began playing snooker at age 7 and soon became a noted amateur competitor, winning his first club tournament at age 9, making his first competitive century break at age 10, and winning the British Under-16 Championship at age 13. At the 1991 English Amateur Championship, aged 15 years and 98 days, he made his first competitive maximum break, then the youngest player ever to do so in a recognised tournament. In the same year, he won the IBSF World Under-21 Snooker Championship and Junior Pot Black.