50 years is a tiny fractional change in the thousands of years of human development.
I am not talking about evolution, I am talking about expectations and social development.
People used to make thier mistakes in thier teenage years because they were able to make those mistakes. They learned earlier and were responsible sooner.
Today most go through the same process in thier 20s.
Consider in many states someone under 18 cannot even get a license anymore or have a similar age passenger without many months of drivers ed. In fact they still cannot drive between 11pm and 5am in California, and cannot have a passenger under 20 for over a year even after they get thier license (which took a minimum of 6 months of a permit and drivers ed courses). Why do they even get a license before 18 anymore?!
A couple generations ago the drinking age was 18 in several states, not 21 like it has become.
Firearms were both available to and used by teenagers on a regular basis.
In fact it starts even earlier. Pre-teens used to be allowed to do things that could result in injury, and required thought.
Today bicycle helmets are mandated by law many places. They cannot play with fireworks. They don't even let them play games like dodge ball and tag many places anymore because they can get hurt. If they role play cops and robbers or pretend to be soldiers etc they can be suspended because it involves pretend guns and weapons.
While children a few generations ago played with slingshots wooden swords, and BB guns, actual weapons, like they play with airsoft today.
Kids used to learn life lessons earlier, they also got hurt more.
Now they are brainwashed and protected from themselves much more.
Now they learn those lessons later in life.
In all age brackets many lessons once learned have been pushed into a later age bracket. So people learn those lessons and gain the responsibility associated with those lessons later in life now.
The result is each age bracket is on average less responsible than they used to be. That extends into the 20s. While most of the same process used to finish by the mid to late teens.