@WhenSunnyGetsBlue
Because you're fixated on notions of discipline too early. If you're doing these things then carry on.
As for when do you start "disciplining": Not in infancy is the answer.
Genuine consequences for "naughty" behaviours start in toddlerhood and build up gradually. So, from the age of about 1 I've been able to say to my child "we don't hit" and move him away from any other child he might be having a little kerfuffle with. Or "books are not for throwing, let's go out into the garden and throw some balls", then you tidy the books. You can say these things in a performative way at the moment, more for the benefit of other parents at playgroup than for your baby- you're just showing them that you're Doing The Thing. But it's a good habit and way of talking to start getting into. An infant is too young for a logical consequence to be tidying up all the books that have been thrown, for example. A young toddler can have that consequence with your help to tidy. At one year old their contribution might be putting one book back on the shelf with lots of praise. My just turned 3 year old (if he ever dared to throw a book!) would be running about to pick them up myself under a stern glare from me and is at the stage of saying "I'm sorry I did X, that wasn't very nice", of his own accord.
You slowly build to more complicated conversations and consequences. There is no set age, you will judge your child's ability to understand things.
By the age of 3 we now have consequences like:
"Oh dear, I see you ripped a page of that library book"
"I'm sorry mummy it was an accident"
"Thank you for saying sorry. Sometimes accidents happen. We need to be gentle with all books, especially library books. What should we do?"
"Daddy can fix it with tape"
"He can, good idea. But I think it would also be nice to say sorry to the librarian too"
"That's a good idea we can do that!"
"Ok we will do that when we return the book. Put it away now and be very careful with your..."
"Books!"
This is a genuine conversation that happened last week with my son who just turned 3 last week. However I have friends with children the same age who are not developmentally ready to understand or respond in the same way. So if I said to my son, "if you don't start showing me that you can play safely with that toy, I will have to remove the toy because someone is going to get hurt and upset. What do you think is a better way to play with the toy?", friends might physically take the toy from their child to get their attention and say "stop throwing or the toy goes away. That might hurt someone."
Also don't be fooled by a child who seemingly understands. Some children like my son can talk the talk but are still only 3 years old. Another toy will be thrown, book ripped, friend pushed etc etc. But they build up a language as a framework to understand things, and you keep your parenting style and consequences consistent or they will find any weakness there and run roughshod over you. I'm not a fan of overly gentle, tip-toeing, softly-softly parenting. Get to the point quickly and follow through with consequences.
So that's my answer to your question. Hope it's helpful.