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.