When do young people become mature enough to make their own decisions? It sometimes seems like a movable feast. Until 1972, voters in Ireland had to be 21 to cast their vote, but it was then changed to 18. In Scotland, 16-year-olds can vote and there is quite a lobby to allow suffrage to 16-year-olds elsewhere, too.
Yet, a new regulation comes into force in Britain this year banning anyone under 18 from purchasing a lottery ticket, due to concern about youngsters being addicted to gambling. In many American states, a young person cannot purchase alcohol - or even enter a bar - before the age of 21.
The age of sexual consent is 17 in Ireland and 16 in Britain, but sometimes blind eyes may be turned to underage sexual activity and there have been many examples of the law being ignored.
Even in the tragic case of Ann Lovett of Granard, which so horrified Ireland back in 1984, it emerged last year that this poor young girl was only 14 (and her boyfriend 16) when they began a sexual relationship.
It would have been protective of the law to issue a warning about complying with the legal age of consent and might even have prevented a dreadful tragedy. But with intimate relationships, the law doesn't always seem keen to intervene.
When it comes to transitioning from one sex to another, it's been a learning curve.
At London's Tavistock Clinic, children as young as 10 had been considered competent to make their own decisions about changing sex - a serious and sometimes irreversible decision.
But then Keira Bell, who had transitioned from female to male at a teenager and then regretted that decision, brought a case against this well-known clinic.
Three High Court judges ruled that children under the age of 13 were not competent to make that choice and even between 14 and 16, it was "doubtful" youngsters could understand the full implications of such a momentous step.
Perhaps drawing a rigid line about when someone is old enough to make personal decisions is complicated because individuals vary so much in the rhythm of their maturing.
I have seen 13-year-old boys handle tractors with great skill - a youngster may drive a vehicle within the bounds of their own property.
But, however skilled that individual kid may be, the age of legal driving on the highway remains 17. And if some are adept at 13, some youngsters are still risk-taking drivers at 17, 18 and above. The line has to be drawn somewhere.
In recent decades, the law has often moved towards being more protective of young people and upping the age for conduct or behaviour that might be considered unwise.
In many countries, the police can apprehend any youngster under 16 seen smoking. And teenagers aren't allowed to buy cigarettes until they are 18 - again, in many American states, until 21.
This is a major change from my childhood days, when I was regularly sent around to the corner shop to purchase 20 Craven A for my mother.
Generally, regulations around alcohol have also shifted, and become more protective - there's research showing the earlier a person starts drinking, the more likely they'll have alcohol problems. The age of sexual consent, too, has been raised over the years. In Victorian times, it was 12 - it took the feminist Josephine Butler to get that changed.
The age of criminal responsibility has also altered in several of jurisdictions in recent years. In Ireland, it was raised from seven to 12 in 2006. Seven was once considered to be "the age of reason" - when a child could tell right from wrong. In Scotland, it was aged eight, until 2019, when it was raised to 12.
In England and Wales, it is 10, although there are campaigns to raise it, as being cruel to charge a young child with legal wrongdoing. Yet the original idea was to discourage "artful dodger" kids being exploited by criminals.
Sometimes, there is a difference between custom and law. Although the age of consent in some European countries was very young - traditionally 12 or 13 in Italy and Spain - there were duennas who chaperoned young maidens, defending them from sexual predators.
On the whole, childhood and adolescence seem to be growing longer. Gone are the days when youngsters were indentured into apprenticeships at 14.
In Gay Byrne's autobiography, he recalls that Guinness's brewery - where his father worked - had a gradation system for their employees, whereby an apprentice would join at 13 or 14, when he would be a "boy". At 18, he'd graduate to a "lad". And at 21, he'd be treated as a full adult employee.
Such hierarchies wouldn't suit our times, but there was a quite sensible idea behind it: that maturing is a process, not an overnight development.
Maybe that's why there's been so much inconsistency in deciding when youngsters are grown-up enough to decide matters for themselves.