I think anyone above the age of eighteen should be matured enough to decide whether he/she should drink or not. But personally I think it is not the age which should be a deciding factor whether an individual should drinks or not...
This is more a question of when you are self dependent. As long as you are in college and studying, do not even think of drinking. When you are employed and tempted to drink, you may. But drinking is no virtue. If you are comfortable without drink, no need to drink.
I think person start drinking if he feel himself alone and start to earn money then when money comes then mind divert to get enjoyment and drinking is one way to utilize money on enjoyment without risk.
Circle of friends also matter to decide whether to drink or not.
It is always not adviseable to a person to have a drink or not? Every person has got his choice of living his lifestyle? Drinking at a younger age will have negative impact on health. It is also adviseable or if possible to avoid the habit of drinking completely.