The Pirates of Penance (1879), the Gilbert and Sullivan comic opera, was cited as a text in the recent decision of PM v Children’s Court of the Australian Capital Territory & Ors  ACTSC 258, a decision of the Supreme Court of the Australian Capital Territory (McWilliam, AsJ).
In PM’s case, the Court had to decide whether PM, who was born in a leap year on 29 February 2000, was 17 and therefore a child at law, or 18 and therefore an adult, when she committed certain criminal offences on 28 February 2018 (being a common year, a non-leap year).
At common law, a person ‘attains an age’ the day before their birthday. This was established in In re Shurey: Savoy v Shurey  1 Ch 268, where a beneficiary under a will who died the day before his 25th birthday, was held to have ‘attained the age of twenty-five years’ and his estate was therefore entitled to the inheritance.
On this basis, PM was 18 years old on the date of the offences.
But s 149 of the Legislation Act 2001 (ACT) provides:
Age in years For an Act or statutory instrument, a person is an age in years at the beginning of the person’s birthday for the age.
PM argued for 1 March, because it would create an anomaly that an anniversary of 29 February is 28 February because the anniversary occurs after only 364 days.
The Director of Prosecutions criticised this argument as one of arbitrary simplicity, citing the argument used to deceive the character of Frederic in W S Gilbert and Arthur Sullivan’s The Pirates of Penzance (who wanted to leave the pirates on his 21st birthday and who was also born on 29 February), into believing that he only had a birthday once every four years:
Though counting in the usual way, years twenty-one I’ve been alive,
Yet reckoning by my natal day, I am a little boy of five! (Act II)
The Court preferred the orthodox construction to the mathematical calculation, and held that ‘birthday’, meaning the anniversary of the date of birth, was the preferred construction. In PM’s case, it was only on 1 March 2018 that she became an adult by satisfying the test of being someone who was ‘at least’ 18 years old.
PM was therefore not 18 at the date of the offences and was entitled to be tried in the Children’s Court, in which mandatory youth justice principles apply, and specific provisions apply for sentencing young offenders.
The Pirates of Penzance had a similarly happy ending, Frederic was released from his apprenticeship and was free to marry Mabel, the Major-General’s daughter.