From the beginning.
It’s generally agreed that this phrase came from American Black English during the middle 1960s. It’s been popular in sports journalism, perhaps because of its catchy, alliterative quality, but also because it’s informal and conversational.
The earliest record of the phrase is from 1966, when it appeared in a story by Toni Cade Bambera, a writer, civil rights activist, and teacher, whose fiction is set in both the rural South and the urban North. How long the phrase may have been used in speech before 1966 is impossible to say.
Another early match is in an article by Louise Moore, Black Men vs. Black Women, in Liberator (August 1966):
“I want to try to explain how we Black women got into this bind. The man’s society is a masculine one that builds itself around the male and his masculine organ. His penis is played up at every opportunity. We see it in the skyscrapers of the cities, the military missiles, the church steeples. He even has one God, one sex, in fact a whole holy trinity of one sex. Poor Mary was given the business. Here’s a woman who has a child and can’t explain how she got it. She took a screwing from the ‘get-go.’”
The phrase may be derived from the older phrase ‘from the word go.’ This expression first appears in the N.A.R.D. Journal (May 10, 1917): “It is a straight, out-and-out business proposition from the word ‘go’; and if druggists will handle it as such, they will have results.” The word ‘go’ here is an indication that it’s the signal to begin a race.
‘From the word go’ originated in nineteenth-century America. Davy Crockett used it in The Life and Adventures of Colonel David Crockett of West Tennessee (1833): “I was plaguy well pleased with her from the word go.”
A related phrase is ‘get going.’ Here’s a quote from Main Street by Sinclair Lewis in 1920:
“She kidded him along, and got him going.”
Some people say that ‘get-go’ is now a cliche, but I like it. It’s short and the alliteration gives it impact. And also because I read a piece playing with the language, which said, “Yeah, that one has been around from the gecko.”
That struck me as funny. Your mileage may vary.