The Late Late Show host struggled with booze throughout the late 1980s and early 1990s, and recently revealed his binges caused him to contemplate suicide in 1991.
Ferguson has now admitted his problems started when he was just a teenager, because he had his first drink when he was a schoolboy.
He tells talk show host Larry King, "I was about 13 years old. And, you know, there was a kind of a culture of it at that time. I think things are a little different in Scotland now. But at that time, I wanted to appear grown up and that was the grown up thing to do.
"Grown-ups were drunks and you wanted to be drunk. By the time I was 18, I was drinking all the time. But, you know, it's very difficult to go to school drunk, even in Scotland in the 1970s. So it was kind of intermittent. But it picked up. My drinking was always unusual."
Ferguson, 47, won his battle with booze and has been sober for the last 17 years.