To be honest, I don't know what we will do. I didn't have a sip of alcohol until I was 18. Not because I wasn't allowed (I actually never asked) but because I didn't want to. I went to parties and saw some of my friends acting silly after drinking and decided I didn't want to do it. That being said, when I did start drinking (when I was about 18.5 I hit it pretty hard as I was living away from home on campus at uni which had a fairly 'fun, drinking atmosphere'. When I say hard it's not like I was drinking every day but when we did go out to drink it was to get drunk.
DH on the other hand started going to parties and drinking from about 16 years of age. I don't think his parents knew. He also did the whole young adult 'lets go out to get drunk thing'.
My sister has been drinking socially since she was about 16ish. My parents knew about it and would let her take a couple of pre-mixed drinks to parties but not enough to get smashed or anything. TBH I think that if my child wanted to have a couple of drinks and were at about the 16 mark I might do the same. It saves them hiding it. I know it might not be the most responsible thing as a parent but if they really want to drink (like with other things) they will do it anyway.