When can we start actual disciplining the child?

I don't remember exactly what my parents did to instil such discipline in me and my brother but it was very clear to us for as long as we remember to adhere to certain rules and to do what was right even in simple things. So I'd say start as early as possible with simple things in setting boundaries, showing cause and effect and exploring teachable moments. The only absolute I can think of is to make sure discipline is coming from a place of love and concern.