哥 is not securely attested as an ancient picture of a brother. Its form is closely connected with 可 and with the early history of 歌, “song”; dictionaries describe a complex path of sound loans and changing meanings before 哥 became the everyday word for an older brother. The two stacked 可 shapes are therefore best treated as a form-and-sound history, not as two brothers in a picture.
A piece of culture
Age lives in the family word Chinese family words often tell you relative age. 哥 means an older brother, while 弟 means a younger brother. The affectionate doubled form 哥哥 is common in both Mandarin and Cantonese. Cantonese also often uses 大佬 (daai6 lou2) for an older brother in everyday speech, depending on family and context.