Being an alcoholic does not define the person, it speaks to the illness of alcoholism. Of course, people can make what they want out of what is or isn't alcoholism.
For some alcoholism is a sham, not a true illness, just a weakness in the alcoholic who cant manage their drink socially.
For others its a complete illness and the alcoholic can't and shouldn't being held responsible ie they are sick.
For most its somewhere in between those two extremes.
The idea though that it takes a certain defined amount of time to become an alcoholic is not held up by most people nowadays. Society has too often seen the teenage alcoholic and drug addict too many times in real life to think alcoholism takes years and years to manifest. Society knows better now. The "Just Say No" educational campaigns of the last 30 years have proven very effective in raising the publics consciousness.
Alcoholism is no respecter of ages, or anything else, for that matter.