A week ago, Associate Justice Verity McWilliam of the ACT Supreme Court pondered a real-life law exam problem:

The plaintiff in these proceedings was born in a leap year, on 29 February 2000. She has been charged with committing certain criminal offences on 28 February 2018, being a common year (or non-leap year). The question on this judicial review application is whether, at the time she allegedly committed those offences, she was 17 and therefore a child at law, or 18 and therefore an adult.

To find that the plaintiff committed her alleged offences when she was (just) a child, McWilliam AJ distinguished not just The Pirates of Penzance but also a High Court judgment. In 1961, a majority of the High Court held that alleged car accident victim Charles John Prowse’s ‘coming… of full age’ occurred at the start of the day before his 21st birthday, citing a strange common law rule. As Dixon CJ explained:

In the anonymous case mentioned in argument in Nichols v. Ramsel the question was in a devise whether the testator was of age or not. The report says “and the evidence was that he was born on the first day of January in the afternoon of that day and died in the morning of the last day of December: and it was held by all the judges that he was of full age; for there shall be no fraction of a day”.

The result was that Prowse, who sued for negligence on the day before his 27th birthday, found his case (just) barred by a six-year statute of limitations that started after his majority.

Justice Windeyer’s judgment in Prowse commenced:

In measuring lapse of time the common law eschews metaphysics. Nevertheless some nice questions have arisen for the courts. In one of the first references to the topic, Dyer’s note of Thomas Somerset’s Case in 1562, it is said “ceo fuit un narrow pinche in le case”. There have been narrow pinches since then.

The pinches include such oddities as how the law deals with time zones, with Windeyer noting that twins speaking on the phone between London and Sydney can potentially speak as ‘adult’ to ‘infant.’ A broader problem is a one-day gap between lay and legal notions of age:

A day, the period of the earth’s axial rotation, is the natural and fundamental division of time. A day for legal purposes is the mean solar day, a period of twenty-four hours. These hours are reckoned from midnight to midnight, the instant of midnight being both the end of one day and the beginning of the next, for there are no rests in time, and as each instant comes it goes. A day has a significance for law in two ways: first, as a division of time, that is the space of time within which an event happened or is to happen, or something was done or is to be done: secondly, as a measure of the passage of time, a unit in a period of time. The distinction tends to become blurred because the passage of time is sometimes spoken of as itself an event, as if it were of the same order as an event that occurs in time. But this is misleading. The birth of a man is an event. His attaining twenty-one is not, in the same sense, an event. It is merely a way of saying that a certain period of time, twenty-one years, has passed since he was born.

While lay people count age by asking how many birthdays they have had, the law counts how many years they have survived. And while lay people treat things done throughout a day as occurring ‘on’ that day, the law treats them (unless relative timing of two events is at issue) as all occurring at the previous midnight. That includes the instant of changing age, which occurs just before midnight at the start of a birthday and is accordingly bumped almost 24 hours earlier:

This is an artificial rule, originally derived by what seems to be mistaken reasoning from the fact that the years of men’s lives are numbered by days and not by fractions of days. The rule, is, moreover, not consistent with the law’s method of computing lapse of time for any purpose unrelated to reaching an age. In that sense it is anomalous. But it has long been a settled rule of law. During the whole of the day before the anniversary of his birth a man is of full age and capacity in law. He is not during that day coming of age. He had come of age when the day began. The days of his nonage had at that instant passed.

Applying Prowse in 1985, South Australia’s Supreme Court ‘reluctantly’ held that a person accused of rape on the day before his 18th birthday must be tried as an adult because he ‘attained the age of 18 years’ at the start of that day.

By contrast, McWilliam AJ was able to distinguish Prowse because the Legislation Act 2001 (ACT) provides that ‘a person is an age in years at the beginning of the person’s birthday for the age.’ She went on to hold that the plaintiff wasn’t an adult (defined as ‘at least 18 years old’) in the ACT until the start of Thursday 1 March 2018. (A specific rule about leap years preserves a Windeyer-esque oddity: had this particular plaintiff been in the Northern Territory, she would have been an adult a day earlier.) Seemingly except for South Australia, all Australian jurisdictions have now legislated to repeal the common law rule, with the 1984 Commonwealth version explaining:

There is a little known legal rule of ancient lineage that a person attains a particular age at the first moment of the day immediately before the anniversary of his birth. This provision abolishes that rule in the case of references to or in Commonwealth Acts and regulations.

But this leaves one national age rule – inserted into s72 of the Constitution by referendum in 1977 (and beyond any parliament’s power to amend – still subject to the common law pinch:

The appointment of a Justice of the High Court shall be for a term expiring upon his attaining the age of seventy years…

As the Commonwealth Solicitor-General once observed in argument before the Court on electoral law, the High Court justices themselves are still subject to the rule their predecessors announced:

The effect of that is that after Prowse v McIntyre and before the amendment, a person in relation to whom an election occurred one day before his or her 18th birthday could vote. The effect of the amendment to the Interpretation Act was to remove that right. So, in fact, of the 1,000-odd days by which the franchise was increased by reducing the age to 21, we have gone back one day since then. Of course, for constitutional purposes the Prowse v McIntyre would remain.

GLEESON CJ: Yes, we are conscious of that.

Of the fifteen former justices appointed since 1977, eight ceased their work on the Court very shortly before their seventieth birthdays, but all delivered their last judgments well clear of their birthday bashes. Cutting things finest were Brennan CJ (see the comment below),  Callinan J, Heydon J and Gleeson CJ himself, who each issued his final judgment exactly two days before his birthday or, as the Dixon Court would have it, on the very eve of his constitutional dotage.