Young Girl In Shorts

In much of Europe and the United States during the 19th and early 20th centuries shorts were worn as outerwear only by young boys until they reached a certain height or maturity. When boys got older, typically around puberty, they would receive their first pair of long trousers. This produced the perception that shorts were only for young boys. Because of this, men would not wear shorts to avoid looking immature. Women tended not to wear shorts in most cultures, due to social mores.
In the 1890s, knee pants (an early type of short pants) became the standard wear for American boys. Many urban school portraits from the 1890s show all but the oldest boys wearing knee pants.
American boys normally wore knee pants with short stockings. This began to change after the 1900s when American boys began wearing knickerbockers, while short pants became more popular in Europe.
In the 30's, shorts started to be worn for casual comfort (e.g. outdoor and athletic activities) by both men and women. However, it was still taboo to wear shorts outside certain activities.