The style of dress was and is a thing but is relative to the standards of the day but the one constant in that was the older, the more 'mature' you were the more sophisticated they tend to be until the point where conventional society sees you as a young adult at which point you would be old enough to work for a wage aka be employed.
Until 1969, in law Adulthood was not said to be fully reached until the age of 21 which corresponds with when you would finish a university degree course and before you both vote and stand for political office.
In 1969 the age of becoming an adult was lowered to 18 years which was reflected in the voting age but it wasn't within recent years that the age to stand for a local authority or as a Member of Parliament was dropped in line with that.
You could leave for work at 14+ until 1972, raised to 15 after then and more recently can only leave before 18 if you have education, training or employment arranged but that would be as a young worker - a older child and paid less.
Thus when we look back at past standards for dress you can easily see why until the late 1960's boys stayed in shorts and girls in pinafore dresses in school because they were seen as very much that and not young adults and they had no need to conform to the same dress and behavioural standards of their parent because society didn't see him as an adult.
Today some boys and girls are pushed into thinking they are older than their years assuming roles that developmentally many are not fully capable of understanding because the brain doesn't stop growing until his early twenties.
In some ways I feel that old standard of adult at twenty one was right although an argument could be made for being able to vote at eighteen as you'd have at least an awareness of the issues and given elections are every four years, the outcome of that would effect you as someone who would become "of age" three years later.
