Background: Norman Clifford Louis O'Neill OAM (19 February 1937 - 3 March 2008) was a cricketer who played for New South Wales and Australia. A right-handed batsman known for his back foot strokeplay, O'Neill made his state debut aged 18, before progressing to Test selection aged 21 in late 1958. Early in his career, O'Neill was one of the foremost batsmen in the Australian team, scoring three Test centuries and topping the run scoring aggregates on a 1959-60 tour of the Indian subcontinent which helped Australia win its last Test and series on Pakistani soil for 39 years, as well as another series in India. His career peaked in 1960-61 when he scored 181 in the Tied Test against the West Indies, and at the end of the series, had a career average of 58.25.
Context: Identified as a future Test prospect, he was selected in a Western Australia Combined XI for a match against the touring England cricket team at the start of the 1958-59 season in Perth. Prior to the match, O'Neill was hounded by the media. The tourists decided to test him with short-pitched bowling, especially Fred Trueman. O'Neill decided to abstain from hooking, while attacking the spin of Jim Laker with a series of sweep shots. After four and a half hours of uncharacteristic restraint, he compiled 104 with an emphasis on off side play. He took a total of 2/67, removing Fred Trueman and Arthur Milton.  He scored 85 against Western Australia and then made 84 not out for New South Wales against England. He was selected for an Australian XI, which played the tourists in a dress rehearsal before the Tests. He made one and two as Australia were crushed by 345 runs.  Nevertheless, O'Neill was selected to make his debut in the five-Test series against England, playing in all of the matches. The First Test in Brisbane was a low scoring match described by Australian captain Richie Benaud as producing "some of the slowest and worst cricket imaginable", O'Neill made 34 in Australia's first innings of 186 to help secure a lead of 52. He then top-scored with an unbeaten 71 in the second innings, guiding Australia to an eight-wicket victory. O'Neill scored 71 of the last 89 runs scored while he was at the crease, refusing to be dried up by the England's usage of leg theory. It enlivened a match plagued by time-wasting, and best remembered for a depressingly slow innings by England's Trevor Bailey, who scored 68 from 426 balls in seven and a half hours. England captain Peter May described O'Neill's innings as "sparkling" and said that it made "everything which had gone before look even more wretched". Retired English player Ian Peebles, writing in the Sunday Times, said "Although O'Neill is in the very early stages of his career, it is already something of an occasion when he comes to the wicket, and one can sense the expectancy of the crowd and the heightened tension of the opposition". Wisden opined that O'Neill had "saved a game that had been tortuous for days". For his part, O'Neill said that the dour play was "unbelievable" and that he was "just about falling to sleep" in the field.  He struck 77 in the rain-affected drawn Third Test at the Sydney Cricket Ground and followed this with 56 in the Fourth Test in Adelaide. Despite making a duck in the Fifth Test, he ended the series as the second highest runscorer with 282 at 56.40 as Australia took the series 4-0. He bowled two overs without success. Outside the Tests, O'Neill scored 155 and 128 against Victoria and Western Australia respectively as New South Wales completed their sixth successive Sheffield Shield win.
Question: How old was he when debuted?. Whats the answer?