Nobody needs to drink.
dolcezza99 Of course they don't, but we don't 'need' to do a lot of things. We don't need to wear clothes that aren't hessian sacks, paint our walls any colour other than white, eat food that tastes nice, take holidays, listen to music, dance, read fiction, keep pets or do anything else that has no purpose other than pleasure. But we still do them because sometimes it's nice to do things purely because we enjoy them.
Nobody is saying you have to drink alcohol if you don't want to but - like it or not - alcohol is a big part of European culture. There are no European countries where being teetotal is standard. So for that reason I think it's useful for people to acclimatise to that.
Getting back to the OP's question, I'd say 14 or 15 is fine for the occasional bottle of beer or glass of wine at home with a meal. I was definitely having the odd drink at home with family or for special occasions from that age onwards. I didn't drink much at all outside of those occasions, though - neither of my two best friends touched a drop of booze until they went to university (because they didn't like it, not because their parents forbade it), so I didn't drink at their houses and we didn't go to the pub very often.
The only thing I would say that I wouldn't offer a teenager sweet, sugary alcopops like WKD, Smirnoff Ice etc. Beer and wine are acquired tastes that most kids don't actually like much at first, so they tend not to knock them back and drink moderately until they actually genuinely like them. I'd rather they had to actually think about what they were drinking rather than be able to thoughtlessly drink them like soft drinks with being particularly aware of what they were drinking.