My oldest only started sleeping through around about 6 to 8 months. My youngest was sleeping through from week 1. I was told to wake kids up to feed them, but after my first experience I realized that causes a huge amount of trouble. So, the second one I left to sleep and fed when she woke up!
My daughter was about two and a half when she started sleeping through reliably. We were okay with that since we coslept with her early on so I didn't have to get up to comfort her if she woke up. She still will come into our bed some nights if she has a nightmare or something, which is fine with us too. I find it kind of strange that I used to get people telling me by what age they thought my kids "should be" sleeping through, as if it affected them in any way. Parents don't need to be pressured about that.
I think this is a tricky one to answer as I've come to realise that in the world of competitive parenting, that sleeping through the night is interpreted differently by different parents. I'd been told of kids sleeping through from 6 weeks but then was later told that this still including waking for feeds. In terms of sleeping through say 7am till 7pm it's also difficult to gauge as the moment you sit back and think you've got a sleeper on their hands something changes to steal your thunder. My eldest slept through really well at 6 months, but then he got a bug, stopped sleeping through and took a while to settle down. A month after that he was sleeping perfectly, and then some more teeth came through, so it was all change again. I think 'sleeping through' is an unrealistic term that puts pressure on parents to ensure their kids go down and stay down, whereas realistic parenting means that if a kid gets up, they're going to get comforted. Both my kids sleep well and have a good sleep pattern, but this can change the moment they get sick, are teething or have had an overly stimulating day.
My first child starting sleeping through the night at about 2.5 years. My second child is getting better, but wakes half the time still and he is 3.5 years. We feel rested though, when he wakes up he will go right back to sleep after we check on him.
From what I can remember daughter 1 was pretty good but can't remember the exact age so it must if been quite early.
Daughter 2 was a nightmare and she was 4 years old and still coming into my bed at night. My husband had been away at sea on and off for the first 4 years of her life then he got a shore job, after 2 nights of her nocturnal visits, he had enough and she was firmly told by hum to sleep in her own bed .., which she did !!
Son was a nightmare but only because he had eczema and that would wake him at night with all the itching. took a good few years with him as well.
my first born started sleeping through at age one using the save our sleep routine for his age. We also moved him into his own room at that time. My 6 month old is now only waking once a night for a feed at 3.30am and he has a 6.30pm bedtime with a 9.30pm dream feed.