I let my dc's have a tiny sip of wine from about age 7. But I have also talked to them about the fact that you can't drink have more than a tiny sip until you are grown up, I have talked about the effects of alcohol on the body, I've talked about the needs even for grownups to be very careful etc. Not in one big ponderous Talk, but now and then, the way we talk about most things in our house.
What they see at home is Mummy and Daddy very occasionally having a glass of wine with a special meal. They see that we have no difficulty in restricting our intake and saving half the bottle to another day. They see alcohol as something that you can consciously exercise control over.
I don't think the very occasional sip is going to do them any harm.
They do know of course that there are other adults that have a much laxer relationship to drink (their paternal grandparents being a case in point!), but I have gently pointed out that there are health risks attached to even a large-regular-but-not-antisocial intake. Also, that if you get into that sort of habit, it does effect the clarity of your thinking (very big off-putting effect on dd, who wants to be a famous author).
Since the whole of the older generation on their father's side drank a fair bit and lived to a ripe old age withouth social problems, I can't overdo it on the scare stories. They won't have to wait until the teenage years to hear the other side. It won't take them a massive effort to work out that dh was brought in a different way, that he is fine, that his dad lived to the age of 93 and was a charming much-beloved gentleman, despite his well-stocked bar cupboard. SO my approach needs to be moderate and good-humoured if I'm not to lose their attention altogether.
I keep remembering that my parents never had alcohol at home and were very uptight about the whole subject, and that didn't stop my db from getting completely rat-arsed at the first teenage party he went to. I think his self confidence is still suffering, 30 years later, from their OTT reaction.
When dd gets to the age of teenage parties I expect we'll chat a bit more about strategies-to-keep-out-trouble-but-still-keep-your-friends.
I don't think not being used to the taste is going to keep a teenager from drinking if they are desperate to impress their friends. If they are confident enough to say 'I don't like wine', then they'd probably be confident enough to say 'I don't want to get drunk'. I see my job as helping to give them that confidence.