When Christine was six months old I started giving her a bottle of water rather than milk if she woke at night. If they're thirsty, they'll drink the water and go back to sleep. She complained for the first few nights about being cuddled and put back down, but within a week she was sleeping through the night.
I didn't need to do it with Sam, she slept through from two months without encouragement, but I will with Max if he is still waking for a 2am feed when he's six months old, also. I reckon that's old enough to cope with an eight hour stretch without milk without it doing him any damage

Kerrie