Some babies can sleep through the night earlier than others. Some babies wake for night feeds til as old as 2 yrs old. My boy slept through the night when he was 6 weeks old but started waking for night feeds again when he was 7 months old. Every baby is different :-) Thats why we must always sleep when baby sleeps :-)
And when baby finally learns to sleep through the night, you will be worrying over whether he's getting enough milk to sustain through the night. Being a mummy has never-ending worries!