My first child slept through the night at 3 months old, she was also bottle fed formula, and she slept in her own room in a crib. She actually preferred the crib to co-sleeping though as we were co-sleeping previous to the crib and she seemed so unsettled and never seemed to be able to get comfortable. I am positive she was sleeping through the night and not waking as we had a baby monitor, kept the bedroom doors open, her crib was on the same wall as our bed, and I am a very very light sleeper.
My second child is currently 26 months old and he has never slept through the night, except a couple months ago for one night when I was out with my hubby for our anniversary lol. Anyways he is still breastfed and co-sleeping.
I think that different factors contribute to sleeping through the night as do the personalities of different children. It is like comparing apples to oranges:)