To latch onto this comment, a lot of countries have slowly increased the age of maturity over time; in my country, the minimum drinking age has gone up to 18 (from 16 for light alcohol), while at the same time the age you can start learning to drive has gone down to 17 or 17,5 (you can practice in simulators at that point iirc). Just to name some examples.

Anyway, I'm pretty sure people are allowed to stay children for longer nowadays, instead of being told to marry and work in the coal mines in their early-to-mid teens.

More cynically / conspiratorial / on the other hand, people are kept infantilized as well as a means of control by various parties in whose interest it is to keep a population docile and dumb. Can't overthrow the government if you've got scantily clad teens to watch.

New Zealand is bringing it down from 20 to 18 at the end of the month. Most restrictions aren't to do with the age of being an adult though.

For example in Britain (age of majority 18, 16 in Scotland)

Sex: 16

Marriage without parental consent: 18, except Scotland (16 for local elections, 16 for Wales coming in next year)

School leaving: 16, but must remain in education outside of school (say official apprentice) until 18

Drinking: 18, 16 in public with a meal when bought by parent, either 0 or 5 at home

Driving: 16 moped + tractor, 17 cars, some vehicles are even higher (23 or 24 for powerful motorbikes for example, 21 for minibusses unless in the army)

Smoking: 18 to buy, 16 to smoke in E+W, 18 to smoke in Scotland

Gambling: 18 (lottery was 16 until recently)

Voting: 18, except in some caes in Scotland where it's 16

Fun fact: in my country the drinking ages are 0, 5, 16 and 18. 18 to buy, 16 to drink with a meal in public, 5 to drink in private and 0 if it's a medical emergency.

Canada does not have states.

I suspect Quebec might be the one that has different rules

For once Quebec is part of the majority in Canada with 18. There are only 4 provinces that set the age of majority at 19 which are BC, NS, NB and NFL.