IMO, the newer the generation, the more immature they get. Back in the 1850s, the twelve-year-old boys were getting guns, hunting, running the farm when Pa is in the next town, etc. The girls were doing all the same responsibilities as the mother. By the time of the 1950s, kids were immature much longer but generally simmered down by the ages of 18-21. Starting with the 1970s and beyond though, adults are running around getting drunk or high every day. Adults tend to be acting immature until they're like 40 now, and that's if they survive that long from too much smoke, overdoses, etc.
