Even young children know what behavior is acceptable or not for adults and children when it comes to alcohol. So you can start talking to them at quite an early age. Parental duties are not taught and there is no child-rearing program. Every child and every family is different and each of us communicates in our own way.
The important thing is to focus on the facts and give your child the knowledge and skills to avoid the risks associated with alcohol. You can explain the effect that alcohol has on the body and the spirit and that even small amounts of alcohol affect our ability to judge and decide rationally.
Also, make sure your child understands why drinking alcohol at an early age is dangerous. Explain that when they come of age they will be able, if they wish, to enjoy reasonable, responsible alcohol consumption in social circumstances.