I just did sleep training with my son a week ago. Hes 5 months and slept through the night all week! Before that he was up 5-6 times a night. It was ridiculous. Now he sleeps 7-7 with nofeeds. My first slept thru the night at 6 weeks. I never realized how lucky i was:)
My son slept through the night only once when he was sick, now I'm trying to teach him to sleep longer periods of time and its working for us, I think if a baby didn't start to sleep through the night by 2-3 months then he/she needs to be taught to do so, otherwise u wont have a good night sleep anytime soon, with my first I really hoped she will outgrow waking up every 2 hours for a feeding but she didn't and I didn't sleep well for 14 months till I weaned her and even after that she would wake up 2-3 times a night to drink water, she still has trouble sleeping through the night at 3 years old.
Mine slept through by 2 months. I double swaddled him so he couldn't move. I let him wake when he was hungry instead of me waking him to eat. He dropped one feeding after a short time and then dropped the second feeding. Good luck!