I think Jim 1 is right. Say 1920 - 1925. Fashion was for longer short trousers as time went on, until the 50's. I wore short trousers until about 1955, they were above knee level but longer than in the images subject of this Thread. Footballers shorts in the 50's were quite long referred to as 'short longs' or 'long shorts', no style whatsoever.