As I turned 31, I was already a raging alcoholic. It was 5 years ago, and I remember my gf at the time taking me to a posh restaurant where I vomited a bottle of red wine into the bathroom sink. There was a bathroom attendant who looked on horrified...poor guy had to clean it up.
So I would tell my 31 yr old self to see the 'writing on the wall' and to recognize that I was in a death spiral. At that time, I had a stomach ulcer from the drinking and I was vomiting in public places, work, and social events frequently. More times than not, I didn't make it to a toilet. I could play the mental games with myself and others, but the booze was clearly affecting my physical health and others started to see that.