My Joshua has been pretty consistent. He's 3 months old. First time he slept through the night he was two months - I was so freaked out when he slept for 6 hours straight (checked on him every 30 minutes... didn't sleep much that night). Since then, every 2 weeks or so, he adds another hour to his sleep. Right now he's just started sleeping 9:30pm-7am, wakes up for a quick feed and then goes back to sleep again until 8:30 when he starts the day. I know, it's odd for a three month old to go that long at night, but he's happy, eating well and napping well, so I'm not going to intervene. :-)
Theressa