Ex-2-wing blunderer here; since 1972 I have exercised my right to vote from places as varied as Hong Kong, NI, Oman, Brunei, Kuwait and, er, West Devon. No point criticising the government of the day if you can't be bothered to take part in the electoral process - I wish we had the Australian compulsory-voting system.
AFAIR, during NS the time to wings was typically about 18-20 months, so we surely must have a Ppruner who had his wings before age 20. Since you could also ask to be called up before 18, he may even have completed his 2 years by the time he was 20.
I just checked various sources on t'interweb (Wikipedia, unusually, not the most helpful for this particular one) and confirmed that writer Frederick Forsyth qualified as an RAF pilot at 19 and went on to fly fighters (Vampire?). He was born in 1938 and left the RAF in 1958, so it looks like 'binbrook' was correct.