When can we start actual disciplining the child?

Start from when the baby starts to crawl!! When kids cannot comprehend language well, use different tones and they are smart enough to understand the difference. Also, if you do not want them to touch certain things, keep it out of their reach. Soon after, they will try different tactics to get things done their way and they stick to whatever works. So if by throwing tantrums, the child gets a balloon/ice-cream, he/she will repeat that tactic in the future. Do not fall for it. You should be the one to set the ground rules and give them a reason for this rule. No perfect rule on how to discipline but it does require lot of patience :)