I started drinking at age 14 and by age 18 I knew that my drinking was DRASTICALLY different than everyone else I knew. I remember taking the "Are you and alcoholic" questionair's and seeing that I qualified. I spend the next 17 years trying to convince myself that the tests where wrong.
For me, I have known that I drink abnormally for a very long time and it did not take long to figure that out.
Just my two cents...