Before the turn of the century men began to wear it in outdoors and sporting pursuits, becoming fashionably worn with teeed jackets. I have not noted turtle necks as boys' wear until about the 1960s. It is quite a flexible style. It can be worn as part of casual clothes, usually during the winter. It also can be worn for informal occasions with a sports jacket or blazer instead of a shirt and tie.
Schools sometimes employ turtle necks as part of a uniform.
I'm not sure what the proper name for this collar was, but boys in the 1920s and30s wore a kind of large open collar. It was an especially popular style in the United States. I have noted it much less commonly in Europe. Other collars Besides these major types of collars worn by boys, there were many other styles that never proved as popular. Mothers and fashion designers could be quite inovative with clooars.